WASHINGTON (AP) The U.S. military on Tuesday pulled off its biggest day of evacuation flights from Afghanistan since the operation began. But deadly violence that has blocked many desperate evacuees from entering Kabuls airport persisted, and the Taliban demanded anew that the evacuation end as scheduled on Aug. 31.

President Joe Biden has been considering whether to extend his self-imposed deadline for completing the airlift, taking into account the continued security threats, the Talibans resistance to an extension and the prospect that not all Americans and at-risk Afghan allies can be evacuated by next Tuesday.

At a news conference in Kabul, Taliban spokesman Zabihullah Mujahid said Tuesday his group will accept no extensions of the deadline.

Amid the tense operation to get people out of the country, CIA Director William Burns secretly swooped into Kabul on Monday to meet with the Talibans top political leader, a U.S. official told The Associated Press.

About 21,600 people were flown safely out of Taliban-held Afghanistan in the 24-hour period that ended early Tuesday, the White House said. That compares with about 16,000 the previous day.

Thirty-seven U.S. military flights 32 C-17s and 5 C-130s carried about 12,700 evacuees. An additional 8,900 people flew out aboard 57 flights by U.S. allies.