Barack Obama has quietly approved guidelines allowing the Pentagon to target Taliban fighters in Afghanistan, US officials have said.
The move broadens previous plans limiting the US military to counter-terrorism missions against al Qaida after this year.
The president's decisions also allow the military to conduct air support for Afghan operations when needed, the officials said.
Mr Obama issued the guidelines in recent weeks, as the American combat mission in Afghanistan draws to a close, thousands of troops return home and the military prepares for narrower anti-terror and training missions for the next two years.
His moves expand on what had been previously planned for next year. One US official said the military could go after the Taliban only if it posed a threat to American forces or provided direct support to al Qaida, while the latter could be targeted more indiscriminately.
"To the extent that Taliban members directly threaten the United States and coalition forces in Afghanistan or provide direct support to al Qaida, however, we will take appropriate measures to keep Americans safe," the official said.
The Taliban's presence in Afghanistan far exceeds that of al Qaida, adding significance to Mr Obama's authorisation. The president's approval came in response to requests from military commanders who wanted troops to be allowed to continue to battle the Taliban, the officials said.
The decision to expand the military's authority does not affect the overall number of US troops that will remain in Afghanistan. Earlier this year Mr Obama ordered the American force presence to be cut to 9,800 by the end of this year, a figure expected to be halved by the end of 2015.
The president wants all US troops to be out of Afghanistan a year later, as his presidency draws to a close.
Some of the Obama administration's planning for the post-2014 mission was slowed by a political stalemate in Afghanistan earlier this year. It took months for the winner of the country's presidential election to be certified, delaying the signing of a bilateral security agreement that was necessary in order to keep US forces in the country after December.