Afghan leader Ashraf Ghani and the head of the country's peace process will meet US President Joe Biden at the White House on Friday, as uncertainty mounts over Afghanistan's future after the American military withdrawal.

Biden has ordered the departure of all US forces from Afghanistan by this year's 20th anniversary of the September 11 attacks that triggered the invasion. In moving to end America's longest war, the president has said he believes that no more can be achieved.

"The visit by President Ghani and Dr Abdullah Abdullah will highlight the enduring partnership between the United States and Afghanistan as the military drawdown continues," White House Press Secretary Jen Psaki said in a statement on Sunday.

She added that Washington is committed to "providing diplomatic, economic, and humanitarian assistance to support the Afghan people, including Afghan women, girls and minorities."  As the US military presses ahead to meet the September 11 deadline, the Taliban have fought daily battles with government forces and claim to have captured 40 districts.

The growing fear and uncertainty about the future have left many Afghans desperate to leave, including thousands of men and women who fear reprisals because they worked with foreign forces. Worries are also heightened that if the Taliban return to power they will reimpose their harsh version of Islamic law, under which girls were banned from school and women accused of crimes such as adultery were stoned to death.

The Taliban said Sunday they remain committed to peace talks but insisted a "genuine Islamic system" in Afghanistan was the only way to end the war and ensure rights -- including for women. "A genuine Islamic system is the best mean for solution of all issues of the Afghans," Taliban co-founder and deputy leader Mullah Abdul Ghani Baradar said.

Talks between the militants and the Afghan government have been deadlocked for months and violence has surged across the country since May when the US military began its final withdrawal. The US pullout from Afghanistan is more than 50 percent complete, the Pentagon said earlier in June. Of special concern are some 18,000 interpreters, commandos and other Afghans who have applied for visas to the United States but are caught in a backlog.

General Mark Milley, the chairman of the US Joint Chiefs of Staff, said earlier this month that "planning is ongoing" to speed the visa process but that the State Department was in charge. State Department officials say they are expediting visas but want to avoid setting off a panicked exodus of educated Afghans.

Last week, the United States hailed a commitment by Turkey to secure Kabul's airport, addressing one key area of concern amid fears the Afghan government will collapse once US forces leave. Turkey, as a Muslim-majority nation but also a member of the Western alliance, has played a key role in Afghanistan since 2001, including by sending troops in noncombat roles and, more recently, welcoming Taliban and government officials for talks on the country's future. The Kabul airport, developed after 2001 with support from the United States and Japan, is seen as crucial to the future of Afghanistan by providing an economic lifeline.