A six-month truce between Israel and the Palestinian Islamist movement Hamas has come into force in the Gaza Strip amid scepticism over how long the Egyptian-brokered deal would hold.

The cease-fire is the first since Hamas took over the impoverished territory just over a year ago.

It's meant to end Palestinian rocket barrages and Israeli reprisals in Gaza that have killed more than 400 people over the past year.

The leaders of both sides expressed hope that the ceasefire would succeed.

Ismail Haniyeh is the Hamas leader.

"The calm will go into effect with the cessation of all Israeli aggression against the Palestinian people. All the Palestinian factions, from their side, are fully committed to it."

He urged an end to what he called "the siege of Palestinian people" and said terminals between Gaza and Israel should be re-opened.

Israeli Prime Minister Ehud Olmert said although he hoped the cease-fire agreement with Hamas would last, he had "no illusions" on it.

"We have no illusions. This calm is fragile and can be short-lived. Hamas and the other terror organizations operating on its behalf have not changed its spots and did not become peace seekers. They still do whatever they can to hurt innocent Israeli citizens."

On Wednesday, a day before the truce took effect, Palestinian militants launched at least 50 rockets and mortars from Gaza. In response, Israel carried out air strikes in the region.