Six Palestinian militants on apparent attack missions were killed by Israeli troops in the northern Gaza Strip late Sunday, shattering a recent calm which has created expectations for the return of the US peace envoy.

Israeli security troops killed three armed Palestinian militants who were trying to enter Israel near the village of Beit Hanun and who, according to army radio, had bombs strapped to their bodies.

"Three armed Palestinians crossed the fence into Israel from the northern Gaza Strip. Security forces saw the Palestinians, called them to stop and tried to arrest them. In response one of them opened fire," according to a statement issued by the office Prime Minister Ariel Sharon.

Just hours earlier, Israeli troops killed three other armed Palestinian militants as they were apparently trying to break into the nearby Jewish settlements of Alei Sinai and Nitzanit, military sources said.

The militants were allegedly trying to smuggle a bag of explosives into the settlements, but were spotted by a patrolling armoured vehicle and killed by a tank shell, they said.

Before the deadly violence, Israeli government officials had said moves were underway to secure the return of US peace envoy Anthony Zinni to the region in a bid to hammer out a ceasefire after 15 months of fighting which has claimed more than 1,100 lives.

Zinni, a retired Marine Corps general, left the Middle East two weeks ago amid raging violence that torpedoed his peace mission.