(KABUL) Western powers are backing the Afghan government's refusal to free hundreds of prisoners accused of some of Afghanistan's most violent attacks, a release demanded by the Taliban as a condition to start peace talks, five sources told Reuters.

The issue is a final major sticking point which, if resolved, is expected to lead quickly to intra-Afghan peace negotiations in Qatar aimed at ending more than 18 years of war in a U.S.-brokered peace process.

"The contentious part right now is the prisoners issue," a senior government source told Reuters. Two European diplomats, an Asian diplomat and another Afghan official confirmed his account.

"There are some dangerous Taliban fighters named in the list, and releasing them is literally crossing a red line," said a senior European diplomat.

"Some NATO members find it extremely uncomfortable to support the release of Taliban prisoners who were behind large-scale suicide attacks on minority groups and on expats."

The Taliban struck a troop withdrawal agreement with the United States in February to pave the way for talks with the Afghan government. But the insurgent group insisted a list of 5,000 prisoners be released.