WASHINGTON, Aug 24 (Reuters) - President Joe Biden told G7 leaders on Tuesday that the United States is on pace to complete the U.S. pullout from Afghanistan by Aug. 31 depending on cooperation from the Taliban, the White House said. Biden sent thousands of U.S. troops to the Kabul airport after the Taliban militant group took over the city and much of the country less than two weeks ago. The nearly 6,000 U.S. troops are helping to evacuate American citizens and at-risk Afghans and to protect the airport so other countries can evacuate their citizens as well. The Pentagon made the recommendation that Biden stick to his Aug. 31 target date on Monday, U.S. officials said. "During a meeting this morning with the G7 leaders, the President conveyed that our mission in Kabul will end based on the achievement of our objectives. He confirmed we are currently on pace to finish by August 31st," White House spokeswoman Jen Psaki said in a statement. Biden told the other G7 leaders that completion of the mission by Aug. 31 "depends on continued coordination with the Taliban, including continued access for evacuees to the airport," she said. "In addition, the President has asked the Pentagon and the State Department for contingency plans to adjust the timeline should that become necessary," Psaki said. U.S. officials told Reuters earlier that the United States has been in regular contact with the Taliban and officials are telling the group that the timeline is contingent on Taliban cooperation. Biden sent CIA Director William Burns to meet Taliban leader Abdul Ghani Baradar in Kabul on Monday in the highest level official encounter since the militant group took over the Afghan capital, a U.S. official and a source familiar with government activity told Reuters on Tuesday. A congressional source said Burns and Baradar had discussed the Aug. 31 date. read more Groups of people wait on tarmac at Kabul"s airport, Afghanistan August 23, 2021. SATELLITE IMAGE 2021 MAXAR TECHNOLOGIES/Handout via REUTERS The Pentagon recommendation reflects increasing security concerns at the Kabul airport, where American citizens and at-risk Afghans are being evacuated. Two U.S. officials, speaking on condition of anonymity, said there was increasing concern about suicide bombings by Islamic State militants at the airport. One official said it was no longer a question of if, but when, militants would attack and the priority was to get out before it happened. Biden was set to speak later on Tuesday. The Pentagon earlier said that it was confident the military can evacuate all Americans who want to leave. Whether thousands of at-risk Afghans would all be evacuated was unclear. "We"re absolutely still aiming towards the end of the month," Pentagon spokesman John Kirby said, while adding that the Pentagon may need additional bases to house evacuees from Afghanistan. Kirby said "several thousand" Americans have been evacuated from Afghanistan but declined to give a more specific figure. He also said he was unable to provide the percentage of Americans in Afghanistan who have now been evacuated. Afghanistan"s new Taliban rulers said on Tuesday they wanted all foreign evacuations from the country completed by Aug. 31 and they would not agree to an extension as Group of Seven leaders met to discuss the crisis. read more Western troops have been working frantically to get foreigners and Afghans onto planes and out of the country and Biden has faced growing pressure from allies to negotiate more time for the airlift. (This story corrects quote in paragraph 6)