Blinken says American diplomats have left Kabul, a stunning turnabout for one of the world’s largest U.S. embassies.

WASHINGTON — American diplomats have left Afghanistan, and the U.S. Embassy in Kabul will remain closed, Secretary of State Antony J. Blinken said on Monday, after the military announced that it had completed its withdrawal from the country.

The disintegration of U.S. diplomacy was a stunning turnabout from plans to stay and help Afghanistan transition away from 20 years of war and work toward peace, however tenuous, with a government that would share power with the Taliban. Earlier this month, Mr. Blinken had pledged that the United States would remain “deeply engaged” in Afghanistan long after the military left.

But that mission was largely dashed on Aug. 15, when the Taliban advanced into the capital, Kabul, forcing President Ashraf Ghani to flee the country and American diplomats to evacuate to a compound secured by the U.S. military at the international airport.

Mr. Blinken’s comments came as the last U.S. military flights departed Afghanistan, carrying a small core of diplomats who had tried to process immigration visas for tens of thousands of Afghans and secure safe passage for about 6,000 American citizens in a two-week evacuation mission from the Kabul airport.

American diplomats will remain engaged in Afghanistan, but from outside its borders. Mr. Blinken said the effort would now be led out of Qatar.

Of paramount importance to the Biden administration are the people — including a small number of U.S. citizens — who were left behind. Mr. Blinken said fewer than 200 were still trying to leave.

Until recently, the embassy in Kabul was one of the largest American diplomatic missions in the world. Just weeks before it closed, and the American flag outside its headquarters was lowered, the embassy’s staff numbered about 4,000 employees, around 1,400 of whom were U.S. diplomats, contractors and officials from other U.S. agencies.

Hundreds of American diplomats had served there after the embassy was reclaimed by Marines in December 2001 during the U.S.-led invasion. It had been closed since 1989, when the Soviet military withdrew from Afghanistan after a 10-year war.

Before Kabul fell, President Biden had promised that the end of the war would bring the departure of American troops from Afghanistan, but not its diplomatic corps. Years of frustrated peace talks were set to continue between the Taliban and the Afghan government, an effort largely fostered by the United States.

“Even as we withdraw our forces from Afghanistan, the United States and our partners remain deeply engaged,” Mr. Blinken said at the State Department on Aug. 2. “Our partnership with the people of Afghanistan will endure long after our service members have departed. We will keep engaging intensely in diplomacy to advance negotiations between the Afghan government and the Taliban with the goal of a political solution, which we believe is the only path to lasting peace.”