President Barack Obama announced Friday that he’s accelerating the U.S. military withdrawal from Afghanistan, with the 66,000 American forces moving this spring into a largely training and advisory role and Afghan troops taking the lead throughout the country in fighting the Taliban-led insurgency.

Obama, addressing a news conference with Afghan President Hamid Karzai after several hours of talks, said the stepped-up pace of the pullout – further details of which are to be revealed in coming weeks – was possible because Afghan forces “continue to grow stronger” through the U.S.-led training and equipping program.

American troops will continue fighting alongside Afghan units when needed, but “their primary mission will be training, advising and assisting Afghan troops,” Obama said. “It will be a historic moment and another step toward full Afghan sovereignty.”

As of the end of September, according to a Pentagon report, Afghan security forces were in the lead in 85 percent of military operations. The transition of U.S. forces to a training and advisory role originally was to have taken place in early summer.