President Joe Biden on Tuesday resisted mounting pressure to keep U.S. troops in Afghanistan past the Taliban's Aug. 31 deadline but ordered his national security team to come up with contingency plans if he determines that a delay is needed.

"The completion by Aug. 31 depends on the Taliban continuing to cooperate, allowing access to the airport for those who we’re transporting out, and no disruption to our operations,” Biden said in an address from the White House. "I’ve asked the Pentagon and the State Department for contingency plans to adjust the timetable, should that become necessary.”

The president has come under withering criticism from lawmakers who say his administration is going to leave behind American citizens and Afghan allies who aided U.S. forces over the past 20 years if the military evacuation mission isn’t extended. Biden promised his administration would spell out on Wednesday how many Americans remain in Afghanistan.