US President Donald Trump told Americans on Tuesday his administration had accelerated talks for a political settlement in Afghanistan and would be able to reduce US troops there as negotiations advance to end America's longest war.

"Great nations do not fight endless wars," Trump said in his annual State of the Union address to Congress, in which he also said US troops had nearly defeated Islamic State militants in Syria and it was time to bring them home.

After 17 years of war in Afghanistan, Trump praised "the unmatched valor" of US forces.

"Thanks to their bravery, we are now able to pursue a possible political solution to this long and bloody conflict," Trump said.

He said his administration was holding constructive talks with a number of groups, including Taliban militants.

"As we make progress in these negotiations, we will be able to reduce our troop presence and focus on counter-terrorism. And we will indeed focus on counter-terrorism," Trump said.

Trump offered no specifics about when he would bring home the 14,000 US troops now in Afghanistan.

US-led forces in 2001 toppled the hardline Taliban for harboring the al Qaeda militants responsible for the September 11 attacks.

"We do not know whether we will achieve an agreement - but we do know that after two decades of war, the hour has come to at least try for peace," Trump said.

'END MILITARY PRESENCE'

The Taliban, responding to Trump's speech, rejected any suggestion of a lingering US focus on counter-terrorism after troops are drawn down, reiterating their long-held demand that all foreign troops get out.

"At the first step, we want all the foreign forces to leave and end the military presence in our country," Sohail Shahin, a spokesman for a Taliban office in Qatar, said by telephone.

"But after ending their military presence, their non-military teams can come and ... take part in the reconstruction and development process."