BAGHDAD — Gunmen believed loyal to radical cleric Muqtada al-Sadr attacked the headquarters of the U.S.-led coalition in Nasiriyah on Friday, trapping some international staffers inside, coalition officials said.

The gunbattle erupted about 7 p.m. between militiamen and Italian troops supported by Filipino security guards, officials said. At least five rocket-propelled grenades were fired at the building over a half hour period.

About 10 coalition staffers, including Italians, Americans and Britons along with 10 drivers and security guards remain trapped in the building, the officials said. Four Italian journalists were also holed up in the building.

Earlier, militiamen pushed their way into the governor's office and were moving near a hotel, a main bridge and police stations.

The tense situation in Nasiriyah developed after daylong fighting in the holy city of Najaf between American force and members of a militia loyal to radical cleric Muqtada al-Sadr.

Coalition officials said there were reports of a scuffle at the governor's office, and that a security guard there was slightly injured.

Al-Sadr's representative in Nasiriyah, Sheik Aws al-Khafaji, threatened attacks on coalition forces, most of whom are Italians.