U.S soldiers stand guard at the airport tower near an evacuation control checkpoint during ongoing evacuations at Hamid Karzai International Airport, in Kabul, Afghanistan, on Wednesday. The U.S. Embassy warns Americans not to go to the airport, citing  security threats.

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U.S soldiers stand guard at the airport tower near an evacuation control checkpoint during ongoing evacuations at Hamid Karzai International Airport, in Kabul, Afghanistan, on Wednesday. The U.S. Embassy warns Americans not to go to the airport, citing security threats. / AP

Updated August 25, 2021 at 8:36 PM ET

The U.S. Embassy in Afghanistan is urging Americans outside the gates of the Kabul airport to leave immediately, citing security threats. Officials also cautioned U.S. citizens against travel to the airport.

"Because of security threats outside the gates of Kabul airport, we are advising U.S. citizens to avoid traveling to the airport and to avoid airport gates at this time unless you receive individual instructions from a U.S. government representative to do so," the embassy said in the Wednesday evening security alert.

"This is a dynamic and volatile security situation on the ground," a State Department spokeswoman said in an emailed statement.

"We take seriously the priority we attach to the safety and security of American citizens. The Embassy in Kabul issued a security alert instructing U.S. citizens who are at the Abbey Gate, East Gate, or North Gate to leave immediately."

The sudden warning came just hours after Secretary of State Antony Blinken said the U.S. would remain "on track" to complete the evacuation mission by the Aug. 31 deadline as long as the Taliban continued to cooperate.

Speaking at a news conference Wednesday afternoon, Blinken underscored the complexity of the operation and its dangers.

"We're operating in a hostile environment in a city and country now controlled by the Taliban, with the very real possibility of an ISIS-K attack," Blinken said, calling the coordinated effort "very high-risk."

Blinken estimated as many as 1,500 U.S. citizens remain in the Taliban-controlled country, though he suggested the number could be much lower.

As of Wednesday, he said, government officials were in touch with approximately 500 people and that officials were providing them with instructions on how to reach the Kabul airport safely.

"For the remaining roughly 1,000 contacts that we had who may be Americans seeking to leave Afghanistan, we're aggressively reaching out to them multiple times a day through multiple channels of communication to determine if they still want to leave," he said, noting that some may turn out not to be American citizens.

Over the last ten days, he said, the State Department has evacuated roughly 4,500 U.S. citizens.

President Biden has called for contingency plans from the Pentagon and State Departments in the event the evacuation mission is not completed in time.

"But let me be crystal-clear about this," Blinken said. "There is no deadline on our work to help any remaining American citizens who decide they want to leave to do so, along with the many Afghans who have stood by us over these many years and want to leave and have been unable to do so. That effort will continue every day past August 31st."

Additionally, Blinken said efforts are "underway on the part of regional countries" to try and keep the airport open past Aug. 31, when U.S. troops are expected to finish their mission.

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