Militants in Hamas-ruled Gaza on Thursday detonated a bomb near an Israeli Army patrol along the border fence, causing no injuries but shaking a fragile truce, an Israeli Army spokeswoman told AFP. "An explosive device was set off against an army force patrolling the fence in central Gaza, south of the Kissufim crossing, causing some damage to the fence but no injuries," the spokeswoman said.

A Gaza witness said that an Israeli ambulance had been at the scene, at the border between Israel and the central Gaza Strip, but the army said nobody was injured.

A second explosion went off minutes later in the same area, but also caused no injuries, the Israeli Army said.

An Egyptian-brokered June 19 truce between Israel and Hamas has virtually halted the violence in and around the Gaza Strip, although militants occasionally still fire rockets and mortar rounds. Hamas has branded those that violate the cease-fire as "collaborators" and said it would punish anyone caught doing so.

Both sides have accused the other of violating the truce, with Hamas demanding Israel lift its embargo of Gaza and Israel accusing the Islamist movement of using the calm to rearm.

Israel, which controls all but one of the entry points into Gaza as well as the sea and air, had agreed to lift its siege of the impoverished territory after the truce was in effect.

Hamas, which won legislative elections in early 2006, took control of the Gaza Strip last summer in bloody street battles between the Islamists and the rival Fatah movement.

Observers say Hamas was spurred into action by reports in the Arab press of an impending US-backed offensive by Fatah to rout the movement from the Gaza Strip.