DAMASUCUS, Syria (AP) — U.N. experts have delayed the start of what's expected to be the last day of their probe into last week's suspected chemical weapons attack near the Syrian capital that reportedly killed more than 300 people.

A convoy of U.N. vehicles left the inspectors' hotel in central Damascus early Friday, but returned minutes later. It was not clear why the team turned back, and the U.N. could not be reached for comment.

The U.N. said Thursday the inspectors would wrap up their investigation Friday into the Aug. 21 attack, and leave Syria the following day. Some of the experts will travel to laboratories in Europe to deliver the material they've collected this week.

The U.S. blames the Syrian government for the attack, and has signaled it could carry out punitive strikes.