(WASHINGTON) — The State Department will begin reducing its staff levels at the U.S. Embassy in Kabul and the Pentagon is sending in troops “as we speak” to help facilitate those departures, the agency said Friday, as Taliban forces advance on more provincial capitals.

Pentagon press secretary John Kirby wouldn’t say the advances took the Biden administration by surprise but said officials are “certainly concerned” by the speed at which the Taliban is moving.

“We’re obviously watching this just like you’re watching this and seeing it happen in real-time, and it’s deeply concerning. In fact, the deteriorating conditions are a factor — a big factor — in why the president has approved this mission to help support our — the reduction of personnel there in Kabul,” he said in a briefing from the Pentagon Friday afternoon.

Kirby said the “leading elements” of one of the two Marine battalions headed to the capital city of Kabul have arrived and that “the bulk” of the 3,000 troops will be there by the end of the weekend.

The U.S. Embassy in Kabul has instructed all U.S. personnel to destroy items like documents and electronic devices to “reduce the amount of sensitive material on the property,” according to an internal notice obtained by ABC News.

“Please also include items with embassy or agency logos, Americans flags, or items which could be misused in propaganda efforts,” the notice said.

A State Department spokesperson is not denying this is the case, but in a statement described things as “standard operating procedure designed to minimize our footprint.”

There wasn’t any specific event that led President Joe Biden and Defense Secretary Lloyd Austin to execute the plan to send troops, Kirby said Thursday afternoon as the crisis escalated, but rather the overall worsening trend in Afghanistan.

“There wasn’t one precipitating event in the last couple of days that led the president and the secretary to make this decision. It’s a confluence of events, and as I’ve been saying for now for several weeks, we have been watching very closely with concern the security situation on the ground — and far better to be prudent about it and be responsible and watching the trends to make the best decisions you can for safety and security of our people than to wait until it’s too late,” Kirby said.

The events in Afghanistan over the last 48 hours, with the Taliban pressuring major Afghan cities, were significant factors in the decision to go forward with the reduction in embassy staffing and the new military mission, a U.S. official told ABC News.

A military analysis said Kabul could be isolated in 30 to 60 days and be captured in 90 days, a U.S. official told ABC News. That timeline seemed even more accelerated Thursday as the Taliban claimed Herat, Afghanistan’s third-largest city. As of Friday, the Taliban had taken control of Kandahar, the country’s second-largest city, located 300 miles south of Kabul and considered the birthplace of the Taliban. The Taliban has also seized Lashkar Gah, the capital of Helmand province.

The U.S. Embassy in Kabul has urged Americans to evacuate Afghanistan immediately, amid fears that the capital could fall into Taliban hands in a matter of weeks.

“Clearly from their actions, it appears as if they are trying to get Kabul isolated,” Kirby said of the Taliban at the Pentagon Friday afternoon.

As the Taliban gained ground Friday, Mick Mulroy, a former deputy assistant secretary of defense, a senior fellow for the Middle East Institute, Afghanistan war veteran and ABC News national security analyst, called on the U.S. to reverse its decision to withdraw troops in order to “prevent the country’s fall to the Taliban and the establishment of a safe haven for terrorist organizations.”

“In the absence of that, the international community must immediately establish a secure, fortified area within the Kabul region where Afghans, especially females, fleeing the Taliban can have their own safe haven,” he said.

“This should also come with a clear warning to the Taliban that if they enter the Kabul region, they will be met by military force from the United States,” he added. “This is the only thing they will understand and likely the only thing that will stop them from an assault on Kabul that will cause a major humanitarian crisis.”

Biden held a meeting with his team Wednesday night and tasked them to come up with recommendations, according to a senior administration official. Then, at a meeting Thursday morning with Austin and national security adviser Jake Sullivan, the recommendations were presented to Biden and he gave the order to move forward.

The official also said the president separately spoke with Secretary of State Antony Blinken Thursday morning to discuss a diplomatic strategy and that Biden continues to be engaged on this issue and is staying in close contact with his team on the situation.

State Department Spokesman Ned Price said the embassy in Kabul will remain open as it reduces its civilian footprint due to the “evolving security situation.” He added that the embassy expects to draw down to a core diplomatic presence in Afghanistan.

“What this is not — this is not abandonment. This is not an evacuation. This is not the wholesale withdrawal,” Price said Thursday. “What this is, is a reduction in the size of our civilian footprint. This is a drawdown of civilian Americans who will, in many cases, be able to perform their important functions elsewhere, whether that’s in the United States or elsewhere in the region.”

The United Kingdom is also sending military personnel — about 600 paratroopers — to Kabul on a short-term basis to provide support to British nationals leaving the country, according to a joint press release from the Ministry of Defence and Foreign, Commonwealth and Development Office. The number of staffers working at the British Embassy in Kabul has been reduced to a core team focused on providing consular and visa services for those needing to rapidly leave the country.

U.K. Defense Secretary Ben Wallace said Friday he believed the country was “heading towards a civil war” as the Taliban gain momentum.

At the Pentagon, Kirby announced Thursday the Defense Department was sending 3,000 troops from three infantry battalions — two Marine and one Army — to Kabul’s Hamid Karzai International Airport to help out with the removal of American personnel from the U.S. Embassy. These numbers are on top of the 650 who were already in Kabul protecting the airport and the embassy.

An additional 1,000 personnel will be sent to assist with the processing of Afghans who worked as interpreters, guides and other contractors and applied for Special Immigrant Visas (SIV).

“I want to stress that these forces are being deployed to support the orderly and safe reduction of civilian personnel at the request of the State Department and to help facilitate an accelerated process of working through SIV applicants,” Kirby said. “This is a temporary mission with a narrow focus. As with all deployments of our troops into harm’s way, our commanders have the inherent right of self defense, and any attack on them can and will be met with a forceful and appropriate response.”

A brigade of 3,000 to 3,500 soldiers from the 82nd Airborne will also be sent to Kuwait to preposition in case they are needed.

Kirby called it a “very temporary mission for a very temporary purpose,” and said the DOD expects to keep no more than 1,000 troops in Kabul to protect the airport and embassy after the Aug. 31 deadline — a number that has notably crept up from the 650 troops originally set to remain.

Price said officials will continue to relocate qualified Afghans who assisted the American mission, such as interpreters and others who worked for the U.S. government, and flights will ramp up in the coming days.

Blinken and Austin spoke to Afghan President Ashraf Ghani earlier Thursday to brief him on the U.S. plans, but the two U.S. officials did not tell Ghani to resign, according to a State Department spokesperson, who added, “Rumors indicating we have done so are completely false. Decisions about who leads the country are for Afghans to make.”

The Taliban have demanded that Ghani resign, in exchange for a reduction in violence and to lay the groundwork for a transitional government. But Ghani has said he is the democratically elected leader of the country and will remain so until negotiations between the Taliban and Afghan government reach a conclusion — an increasingly distant reality.

Shabia Mantoo, a spokesperson for the United Nations High Commissioner for Refugees, warned Friday at a press conference in Geneva that a worsening humanitarian crisis is unfolding in Afghanistan.

“The human toll of spiraling hostilities is immense. The United Nations Assistance Mission has warned that without a significant de-escalation in violence, Afghanistan is on course to witness the highest ever number of documented civilian casualties in a single year since the UN’s records began,” she said.

U.N. Secretary-General António Guterres called for a cease-fire in remarks on Friday.

“The message from the international community to those on the warpath must be clear: seizing power through military force is a losing proposition,” he said. “That can only lead to prolonged civil war or to the complete isolation of Afghanistan.”

“I call on the Taliban to immediately halt the offensive and to negotiate in good faith in the interest of Afghanistan and its people,” Guterres continued.

According to the U.N., some 400,000 civilians have been forced to flee from their homes since the start of the year, joining 2.9 million Afghans already internally displaced across the country at the end of last year, she said.

ABC News’ Cindy Smith, Justin Gomez, Guy Davies and Molly Nagle contributed to this report.

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