Army Gen. John Nicholson, the commander of Resolute Support forces and US forces in Afghanistan, discussed the US’s new strategy for Afghanistan at a news conference in Kabul, Afghanistan, on Thursday. REUTERS/Omar Sobhani KABUL, Afghanistan — The top US military commander in Afghanistan on Thursday said President Donald Trump's new strategy was 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.

"The Taliban cannot win on the battlefield — it's time for them to join the peace process," Gen. 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 during the 2016 presidential campaign, have argued that Afghanistan is no closer to peace despite billions of dollars spent on aid and nearly 16 years of US and allied military operations.

In February, Nicholson told the US 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, though neither he nor his military leaders have provided any specifics about troop numbers or timelines.

The US force for the predominantly advise-and-assist mission in Afghanistan stands at about 8,400, well down from about 100,000 during the "surge" decided on by Trump's most recent predecessor, Barack Obama.

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

Nicholson said new advisers from the US 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 US-backed Afghan forces in late 2001, but US forces have been bogged down there ever since. About 2,400 US troops have been killed in Afghanistan.

US military and intelligence officials are concerned that a new Taliban victory would allow Al Qaeda and the Islamic State's regional affiliate to establish bases in Afghanistan.

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

(Writing by Josh Smith; Editing by Paul Tait)