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The Obama administration is considering a plan that would allow the U.S. military to strike more targets with fewer restrictions throughout Afghanistan, officials told NBC News on Thursday.

A senior U.S. official said active discussions are under way to give U.S. forces new authority to strike Taliban fighters simply for being part of the Taliban.

Under current authority, they may carry out strikes only in self-defense, to protect Afghan forces deemed to be in imminent danger or to target al Qaeda and ISIS.

A senior defense official said the military has been "advocating" to expand its mandate, noting that the Taliban made significant advances last year and that Afghan forces couldn't keep up.

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Afghan security forces during an operation last week against Taliban fighters in Helmand province. Watan Yar / EPA

Targeting Taliban assets in general could help Afghan forces take back territory, particularly in Helmand and Oruzgan provinces, where the Taliban have shifted much of their effort recently, this official said.

The defense official said the discussion is related to a pending decision about how many troops the Obama administration will keep in Afghanistan after 2016. There are currently 9,800 U.S. troops there, but that's planned to shrink to about 5,500 by the end of the year.

The new authority wouldn't require an increase in U.S. troops, said the official, who added, "We expect a positive outcome."

U.S. officials told NBC News last month that the appointment of new leaders of the Taliban could mean more attacks on U.S. targets.

Related: Haibatullah Akhundzada Named New Leader of Afghan Taliban

In an open letter this week, five former military commanders in Afghanistan and five former ambassadors to Afghanistan urged President Barack Obama not to reduce the U.S. presence before he leaves office next January.

The signatories included retired Army Gens. John F. Campbell, who relinquished command of the war in February, and David Petraeus, who later became director of the CIA, and former Ambassador Zalmay Khalilzad, who was also President George W. Bush's ambassador to the United Nations.

The current rules have been in place since the Obama administration declared an end to the combat mission in Afghanistan in December 2014. But there is precedent for the plan under discussion: Earlier this year, the administration gave the U.S. military the legal authority to strike ISIS there.

Asked about the proposed plan Thursday, Pentagon press secretary Peter Cook said, "We are always looking at the authorities question and the best use of our troops."