The first forces of a Marine battalion arrived in Kabul at week’s end to stand guard as the U.S. speeds up evacuation flights for some American diplomats and thousands of Afghans, spurred by a lightning Taliban offensive that increasingly is isolating Afghanistan’s capital.

Pentagon spokesman John Kirby said “elements” of a battalion were now in Kabul, the vanguard of three Marine and Army battalions that the U.S. was sending to the city by the end of the weekend to help more Americans and their Afghan colleagues get out quickly.

The Taliban, emboldened by the imminent end of the U.S. combat mission in the country, took four more provincial capitals Friday, heightening fears they would move soon on the capital, which is home to millions of Afghans. “Clearly from their actions, it appears as if they are trying to get Kabul isolated,” Kirby noted at a Pentagon briefing.

The Pentagon also was moving an additional 4,500 to 5,000 troops to bases in the Gulf countries of Qatar and Kuwait, including 1,000 to Qatar to speed up visa processing for Afghan translators and others who fear retribution from the Taliban for their past work with Americans, and their family members.

The remainder — 3,500 to 4,000 troops from a combat brigade of the 82nd Airborne Division — were bound for Kuwait. Kirby said the combat troops would be a reserve force on standby “in case we need even more” than the 3,000 going to Kabul.

The temporary buildup of troops for U.S. evacuations highlights the stunning pace of the Taliban takeover of much of the country, less than three weeks before the U.S. is set to officially end nearly 20 years of combat in Afghanistan. President Joe Biden has remained adamant about ending the U.S. mission on Aug. 31.

Friday’s latest significant blow was the Taliban capture of the capital of Helmand province, where American, British and other allied NATO forces fought some of the bloodiest battles in the past 20 years. Hundreds of Western troops died there during the course of the war, in fighting that often succeeded in knocking back Taliban fighters locally, only to have the Taliban move back in when a Western unit rotated out.

The State Department said the embassy in Kabul will remain partially staffed and functioning, but Thursday’s decision to evacuate a significant number of embassy staff and bring in the thousands of additional U.S. troops is a sign of waning confidence in the Afghan government’s ability to hold off the Taliban surge. The Biden administration has not ruled out a full embassy evacuation.