The Biden administration is set to begin evacuations of Afghans who aided the U.S. military effort in the nearly 20-year war during the last week of July, according to a senior administration official.

The Operation Allies Refuge flights out of Afghanistan will be available first for special immigrant visa applicants already in the process of applying for U.S. residency, according to the official, who was not authorized to comment publicly and spoke on condition of anonymity.

President Joe Biden has faced pressure from lawmakers on both sides of the aisle to come up with a plan to help evacuate Afghan military helpers ahead of next month’s U.S. military withdrawal.

The White House began briefing lawmakers on the outlines of their plans last month.

The evacuation planning could potentially affect tens of thousands of Afghans. Several thousand Afghans who worked for the U.S. — plus their family members — are already in the application pipeline for special immigrant visas.

The Biden administration has also been working on identifying a third country or U.S. territory that could host Afghans while their visa applications are processed.

The administration is weighing using State Department-chartered commercial aircraft, not military aircraft, according to a second administration official, who spoke on condition of anonymity to discuss internal deliberations. But if the State Department requests military aircraft, the U.S. military would be ready to assist, the official said.

Tracey Jacobson, a three-time chief of mission in Tajikistan, Turkmenistan and Kosovo, is leading the State Department coordination unit that will deliver on the president’s commitment under Operation Allies Refuge. That unit also includes representatives from the defense and homeland security departments.

Russ Travers, deputy homeland security adviser and former head of the National Counterterrorism Center, is coordinating the interagency policy process on Operation Allies Refuge, officials said.

Separately, the White House announced that Elizabeth Sherwood-Randall, the White House homeland security adviser, would lead a U.S. delegation to a security conference in Uzbekistan this week to discuss Afghanistan’s security issues with leaders from the Central 5 — Austria, the Czech Republic, Hungary, Slovakia and Slovenia —and other regional players.

Afghan President Ashraf Ghani and Zalmay Khalilzad, U.S. special envoy on Afghanistan reconciliation, are also expected to take part in the conference.

Biden announced last week that the U.S. military operation in Afghanistan will end on Aug. 31.

The firming of the date to end the war comes after former President Donald Trump’s administration negotiated a deal with the Taliban to end the U.S. military mission by May 1, 2021. Biden, after taking office, announced that U.S. troops would be out by the 20th anniversary of the Sept. 11, 2001, attacks. The attacks were plotted by al-Qaida leader Osama bin Laden from Afghanistan, where he had been given refuge by the Taliban.