Al Jazeera has found evidence of a possible mass execution of political activists in Libya.

Visiting a hospital in Tripoli on Thursday, Al Jazeera's James Bays said he saw the bodies of 15 men suspected to have been killed a few days earlier as the rebels closed in on the Libyan capital.

"The smell here is overpowering," Bays said from the hospital where a number of bodies lay.

"I have counted the bodies of 15 men we were told there were 17 here. Two bodies were taken away by relatives for burial."

"We are told these men were political activists who have been arrested over the last few days and weeks and being held near the Gaddafi compound. When the opposition fighters started to enter the compound we are told they were killed.