Several hundred US troops have left Afghanistan, on the same day President Joe Biden decided not to extend the August 31 evacuation deadline, Pentagon press secretary John Kirby confirmed Tuesday evening. “These troops represent a mix of headquarters staff, maintenance and other enabling functions that were scheduled to leave and whose mission at the airport was complete. Their departure represents prudent and efficient force management. It will have no impact on the mission at hand,” Kirby said in a statement, confirming CNN’s earlier reporting from two defense officials that the US’ troop withdrawal from Afghanistan had kicked off. The fact that a small number of American troops have already left underlines how quickly the situation is moving. The pace of evacuations has rapidly ramped up in recent days but with a week until Biden’s deadline, the US military will soon be forced to switch from transporting Americans and Afghans out to concentrating on safely moving all the troops out and winding down the security operation at the airport. “So far, the reduction does not affect the mission,” one of the officials said, adding that the commander on the ground can decide what military personnel are in units that are no longer required. That decision can be based on a few factors, including the number of gates open at the airport, the number of people coming through and more. “If you can have a smaller mission set and still conduct the mission, then you can reduce your footprint and reduce your risk,” the official said. The Pentagon has been acutely aware of the threat posed by ISIS-K and other terror groups around the airport, developing alternate routes to the field for US citizens and Afghan evacuees. In addition, the Taliban have stated openly that they do not want a US military presence in Afghanistan beyond the end of August, warning that there will be “consequences” were the US to stay longer. In remarks to an emergency meeting of the G7 on Tuesday, Biden said the threat to US troops in Kabul was one of the key reasons he was sticking to the end of the month as the final withdrawal date. “There was strong agreement among the leaders, both about the evacuation mission underway as well as the need to coordinate our approach to Afghanistan as we move forward,” Biden said at the White House Tuesday afternoon. White House press secretary Jen Psaki had said in a statement earlier Tuesday that “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 and provided an update on progress in evacuating Americans who want to come home, third-country nationals, and Afghans who were our allies during the war.” Psaki said Biden noted that each day the risks are getting higher in a country now controlled by the Taliban and made a particular point of warning of the potential for terror attacks, which has become an acute concern inside his administration. “There has been no change to the timeline of the mission, which is to have this completed by the end of the month,” Kirby said Tuesday morning. “If the worst-case scenario were to happen, you don’t want more people there than you need,” the defense official said. Biden ‘mindful of the increasing risks’ But the President also said Tuesday he’s asked for contingency plans to adjust the August 31 timetable, “should that become necessary.” However, he stressed that each day American troops are in the country brings “added risk.” “I’m determined to ensure that we complete our mission, this mission. I’m also mindful of the increasing risks that I have been briefed on and the need to factor those risks in. They’re real, and significant challenges that we also have to take into consideration,” he continued. As the US nears the final date of withdrawal, the number of Afghan evacuees flown out is expected to gradually decrease, while the number of US troops flown out is expected to increase. Biden said Tuesday that 70,700 people have been evacuated from Afghanistan since August 14 and that the US is on pace to finish its evacuation mission by August 31. “The sooner we can finish the better,” he said, adding that in the past 12 hours, 19 US military flights evacuated approximately 6,400 people and 31 coalition flights carrying 5,600 people have left Kabul. The State Department has contacted all Americans who were registered in Afghanistan and instructed them to report to designated locations for evacuation, according to a source familiar with an administration “SitRep” from Tuesday morning. The source said the “SitRep” acknowledges US citizens “have experienced delays at checkpoints” but that they have “eventually” reached the airport in Kabul, and noted that US citizen evacuations are ongoing. The State Department also sent a push message to all Americans in Afghanistan saying that if they do not choose to leave they should be “prepared to arrange their own departure,” according to the message reviewed by CNN. About half an hour later, however, the agency sent a message recalling that guidance. It was not immediately clear why the State Department recalled the message. CNN has asked the department for comment. Desperate situation But even as the United States flies tens of thousands of people out of the country, many Afghans who assisted the war effort are still awaiting their turn to leave. Many Afghan allies who the US has aimed to help will be left behind, a senior administration official told CNN, adding, “That would be true whenever we evacuated and whenever the Taliban took over.” The official said the 70,000 people evacuated in the last 10 days do not closely match the universe of Afghan allies eligible to come to the US, which Biden has previously estimated at 50,000 to 65,000. Many of the 70,000 evacuated have included different groups of Afghan allies given priority by the US’ European partners. In addition, some of those evacuated have not even applied for Special Immigrant Visa status yet, though they will in Qatar or Kuwait. The official declined to estimate the number of Americans still in Afghanistan, deferring to Secretary of State Antony Blinken, who will speak Wednesday, but said the number on August 14 was “probably lower than most people believe” because “a lot left in the final few weeks.” This story has been updated with additional information Tuesday.