KABUL, Afghanistan (Reuters) – U.S. and Taliban negotiators wrapped up their longest round of consecutive peace talks on Tuesday with progress made but no agreement on when foreign troops might withdraw, multiple sources said.

The 16 days of talks, in which the United States also sought assurances that Taliban insurgents will not use Afghanistan to stage attacks, are expected to resume in late March.

“Withdrawal of the foreign forces and the guarantee that Afghanistan will not be used (to attack) any other country were the only two topics of discussion,” a source familiar with the meetings said.

The negotiations in Doha, Qatar included the Taliban's political chief Mullah Abdul Ghani Baradar and a U.S. negotiating team led by special envoy Zalmay Khalilzad.

Khalilzad is now expected to travel back to Washington to brief U.S. officials, the sources said.

Around 14,000 U.S. troops are based in Afghanistan as part of a U.S.-led NATO mission to train, assist and advise Afghan forces. Some U.S. forces also carry out counter-terrorism operations.

(Reporting by Jibran Ahmad in Peshawar, Eric Knecht in Doha and Abdul Qadir Sediqi in Kabul; Writing by Rupam Jain and Rod Nickel in Kabul; Editing by Mark Heinrich)