Gaza militants on Monday said they were committed to a truce with Israel but the day-old ceasefire appeared shaky as four rockets hit the Jewish state.
No injuries or damages were reported from the rockets that hit open fields around the southern cities of Beersheva, Sderot and Ashkelon, police said, noting a Grad rocket fired at Beersheva was intercepted by the Iron Dome defence system.
Earlier on Monday, Palestinian factions said they were committed to a truce with Israel, but were still primed for a possible escalation after weekend clashes killed 13 people, all but one of them Palestinians.
"We are committed to the truce but if the Israeli aggression in Gaza increases, we will expand the shelling area," said Abu Ahmad, a spokesman for Al-Quds Brigades, the armed wing of Islamic Jihad.
The group was at the centre of the deadly weekend flare-up, with nine of the 12 Palestinians killed in Israeli air strikes identified as Islamic Jihad militants. Rockets fired by the group also killed an Israeli man.
The rocket fire tailed off early on Sunday after the Egyptian-brokered truce took effect, but overnight five projectiles hit southern Israel, police said, landing in open areas without causing any harm.
On Monday morning, the bodies of two Palestinian militants were found in southern Gaza, local medics said, raising to three the number of Palestinians killed by Israel since the start of the truce.
The two belonged to a small faction called Al-Ansar Brigades, which is understood to be close to Gaza's ruling Hamas movement.
The discovery raised to 13 the total number of people killed in 36 hours of clashes in and around Gaza, including three militants who died in two air strikes which occurred after the truce was put in place.
But Israeli Defence Minister Ehud Barak said he hoped the spike in violence had passed, saying: "Islamic Jihad has received a heavy blow," although Israel would not hesitate to carry out a major operation in Gaza if the need arose.
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"I don't rule out the possibility that the time will come for a broad and full-scale confrontation," he told army radio.
"I don't miss being in Gaza, and I don't know anyone who knows what will be there after the Hamas government falls."
Matan Vilnai, minister for home front security, told public radio the military had focused its energies on Islamic Jihad.
"Hamas does not want a confrontation," he said, indicating the Islamist movement was awaiting the release of 550 Palestinians in the second stage of a prisoner swap deal which on October 18 saw Hamas freeing Israeli soldier Gilad Shalit in exchange for 477 detainees.
Meanwhile, Al-Quds Brigades said it had for the first time used a rocket launcher mounted on the back of a truck capable of firing multiple rockets in quick succession.
Footage shown on its website showed five Grad rockets being launched into Israel, with analysts suggesting the new mobile launchers could have been brought in from Libya.
"The Arab Spring -- especially what happened in Libya and Egypt -- helped in transferring weapons to the resistance here," said Walid al-Mudalal, a professor of political science at the Islamic University in Gaza.
The new hardware would allow militant groups to "outsmart the Israeli security doctrine and transfer the battle to the enemy's territory," he said, indicating they would now be able to hit even deeper into southern Israel.
Mukhaimer Abu Saada, a political scientist at Gaza's Al-Azhar University, said the rocket launcher in the video could be "from Libya" given the large number of jeeps which had been smuggled into the strip over the past year.
But obtaining mobile rocket launchers was not tantamount to strategically "accomplishing a balance of terror," he said, warning Israel could use it as a pretext "to prepare for a massive blow" against Gaza.