SAN JUAN, Puerto Rico?A mob armed with bats and pipes attacked 10 U.S. Navy Marines, leaving one with a cranial fracture and others with injuries from broken bones to minor scrapes, the Navy said Tuesday.

All 10 were released from the hospital Tuesday after a brawl that erupted Monday night in the colonial section of San Juan, capital of this U.S. Caribbean territory, said Lt. Corey Barker, a Navy spokesman.

The Marines?more than 60 wearing civilian clothes at the time?had just finished work as a security detachment for contested military exercises on the outlying island of Vieques.

Two Marines were arguing between themselves outside at about 11 p.m. when the armed mob started attacking them, Barker said.

The attackers fled and police were unable to make any arrests.

The Marines are expected to return to their duties on the mainland this week.