It is up to the Afghan people alone how they run their country, President Joe Biden on Thursday said as he announced the U.S. military mission in Afghanistan will end on Aug. 31 despite new concerns about the possibility of a civil war.

“We did not go to Afghanistan to nation-build,” Biden said. “It’s the right and the responsibility of the Afghan people alone to decide their future and how they want to run their country.”

Biden conveyed his most extensive comments to date about the U.S. withdrawal from Afghanistan under pressure from critics to give more explanation for his decision to withdraw.

Biden also said U.S. plans to move thousands of Afghan interpreters out of the country in anticipation of the end of the U.S. military mission in the country on Aug. 31.

The Pentagon says the withdrawal of U.S. forces is 90 percent complete.

Washington agreed to withdraw in a deal negotiated last year under Biden’s Republican predecessor, Donald Trump.