Hamas announced Thursday that a unilateral cease-fire on the part of all factions in the Gaza Strip was to come into effect at 11 P.M. local time.

Officials in Hamas said that the decision was made following a meeting between all Gaza factions.

The Hamas offer comes as fighting flared in Gaza on Thursday after a Palestinian anti-tank missile hit an Israeli school bus, wounding two, and Israeli forces retaliated with planes and artillery, killing five Palestinians.

Palestinian medics said at least 30 people were injured in three hours of attacks by Israeli forces. Firing tapered off after nightfall.

Open gallery view IDF strike on Gaza Strip. Credit: AFP

A 50-year old Palestinian in east Gaza was killed by shelling in the afternoon and four others were killed by air attacks in the south near the border with Egypt.

A 16-year-old Israeli boy on the bus was seriously wounded and its driver was injured.

Armed Islamist movement Hamas, which has ruled Gaza since 2007, took responsibility for the attack on the bus, saying it was retaliating for Israel's killing of three Palestinian militants in an air strike on Saturday.

An Israeli F-16 warplane bombed a major security compound of the Islamist Hamas group which rules Gaza, rocking Gaza City with a big explosion and wounding at least one person there.

"We hope this situation will be contained, but we will not shy away from taking all the necessary action, offensive and defensive, to protect our country and to protect our citizens," Prime Minister Benjamin Netanyahu told a news conference during a visit to Prague.

The IDF said 45 rockets and mortars were launched into Israeli territory from Gaza in the space of three hours, the heaviest fire in two weeks. There were no immediate reports of further Israeli casualties as a result.

Palestinian President Mahmoud Abbas urged Western powers to intervene "to stop this aggression", the official Wafa news agency reported from Ramallah in the West Bank.

Abbas also urged Palestinian militants not to give Israel an excuse to hit Gaza.

The missile attack followed a relative lull in cross-border fire between Gaza and Israel after a sudden rise in violence last month in which at least 16 Palestinians were killed.

Israel and Hamas had signaled readiness to return to a de facto ceasefire which has kept the border relatively quiet since the end of the December 2008-January 2009 Gaza war.

A Hamas spokesman on Thursday repeated that his movement wants "calm" to return to the tense standoff.