"We're going down to 8,600 and then we make a determination from there," Trump said in an interview with Fox News radio. "We're always going to have a presence."

Trump also warned that if another attack on the United States originated from Afghanistan "we would come back with a force like ... never before."

The comments provided some clarity on US intentions after lengthy negotiations with the Afghan guerrilla group over finding an exit from a war that has lasted two decades.

Despite overwhelming advantages in firepower, the US military has little to show for its efforts and Trump is hoping he can declare the war over in time for his 2020 reelection campaign.

Washington has been talking to the Taliban since at least 2018, with the main sticking point being how to get sufficient guarantees that Taliban territory will not be used by Al-Qaeda or other international militant groups to plot attacks on the United States.

There are currently around 14,000 US troops in the country, a number already far down from a peak of around 100,000.

The Taliban want all US troops out. But Trump underlined that there was to be no complete withdrawal, keeping a force that would provide "high intelligence."

"You have to keep a presence," he said.

- 'Not based on trust' -

It is unclear what a US pullback will mean for the Afghan government, whose own US-trained armed forces risk a renewed onslaught from the Taliban.

For now, the White House appears to be focusing on ensuring US security, especially with regards to making sure that the Taliban keep their side of the bargain.

"We're well aware of the history of the Taliban ... and its complicated history with Al-Qaeda, which is exactly why any deal, if one is reached, will be so stringently monitored and verified," a State Department spokesman said.

"The agreement we're working on is not based on trust -- it will be based on clear requirements and commitments, subject to our monitoring and verification."

US forces were first sent to Afghanistan after the September 11, 2001 terrorist attacks on US soil carried out by Al-Qaeda, which was sheltered by the former Taliban regime. About 2,400 US troops have died there and around 20,000 have been wounded.

Summing up the cautious US position in the Taliban talks, General Joseph Dunford, chairman of the Joint Chiefs of Staff, said Wednesday that he would not call the process a "withdrawal."

"I'm using 'we're going to make sure that Afghanistan is not a sanctuary, and we're going to try to have an effort to bring peace and stability to Afghanistan,'" he said.