Israeli tanks rolled into the West Bank city of Hebron early Thursday, firing in all directions, Palestinian witnesses said. But it was unclear if the move signaled a full-scale invasion of the city.

The Israeli military had no immediate comment. The witnesses counted seven or eight Israeli tanks moving about half a mile into the city, in the southern part of the West Bank.

During Israel's large-scale military operation in the West Bank, which began March 29 in response to a series of Palestinian suicide bomb attacks, Hebron was left alone while Israeli forces entered most of the other main Palestinian population centers.

Hebron is a constant source of tension. It is the only West Bank city divided into Israeli and Palestinian zones, as Israeli forces control a section of the city where about 450 Israeli settlers live in three enclaves. There are frequent clashes between the two sides.

On Monday, a Marwan Zalloum, the commander of the Al Aqsa Martyrs' Brigade militia, and his bodyguard were killed in an Israeli helicopter missile attack. Israel said Zalloum was responsible for a string of attacks against Israelis, including the gunfire death of a 10-month-old baby in one of the Jewish enclaves in the city.