KABUL (Reuters) - The top U.S. military commander in Afghanistan said on Thursday President Donald Trump’s new strategy is a sign of a long-term commitment to what is already America’s longest war and called on Taliban insurgents to agree to peace talks.

U.S. Army General John Nicholson, Commander of Resolute Support forces and U.S. forces in Afghanistan, speaks about the U.S. new strategy for Afghanistan during a news conference in Kabul, Afghanistan August 24, 2017. REUTERS/Omar Sobhani

“The Taliban cannot win on the battlefield, it’s time for them to join the peace process,” General John Nicholson told reporters in the Afghan capital, Kabul. “We will not fail in Afghanistan, our national security depends on that as well.”

Critics, including Trump himself during the 2016 campaign for the U.S. presidency, have argued that Afghanistan is no closer to peace despite billions of dollars spent on aid and nearly 16 years of U.S. and allied military operations.

In February, Nicholson told the U.S. Congress he needed “a few thousand” more troops in Afghanistan, mostly to help advise Afghan security forces that are battling Taliban, Islamic State and other Islamist insurgents.

Trump has now approved an extended American presence in Afghanistan, although neither he nor his military leaders have provided any specifics about troop numbers or timelines.

The current U.S. force for the predominantly advise-and-assist mission in Afghanistan stands at around 8,400, well down from around 100,000 during the “surge” decided on by Trump’s predecessor, Barack Obama.

Several thousand more troops are often in the country on “temporary” or other uncounted missions.

Nicholson said new advisers from the United States and NATO coalition allies would increase the training missions, including at specialized military schools and expanding the Afghan air force and special forces.

He also praised Trump’s decision not to impose “arbitrary” deadlines on the American mission in Afghanistan.

“This policy announcement ... is proof of our continued commitment,” he said.

The Taliban government was overthrown by U.S.-backed Afghan forces in late 2001 but U.S. forces have been bogged down there ever since. About 2,400 U.S. troops have been killed in Afghanistan.

U.S. military and intelligence officials are concerned that a new Taliban victory would allow al Qaeda and Islamic State’s regional affiliate to establish bases in Afghanistan.

That could allow them to plot attacks against the United States and its allies, they fear, just as Osama bin Laden had done with the Sept. 11, 2001, strikes that triggered the war in Afghanistan.