Gaza fighters fired dozens of shells into Israel Saturday, reportedly wounding at least two people, while Palestinians said five had been hurt in Israeli air strikes.
The armed wing of the Hamas resistance movement governing the Palestinian territory said it had mounted the attack, three days after an Israeli air strike killed two of its members in the Gaza Strip.
Israel said 49 mortar bombs fell on or around Israeli communities near the border with the Gaza Strip.
Army radio said only minor damage was caused but an Israeli military spokesman said two were lightly wounded when three projectiles fell on Pithat Shalom in the Negev desert.
Two more had hit Eshkol, further north, causing neither damage nor casualties, the spokesman said.
Israeli radio said residents were advised to take shelter until further notice.
The Palestinian Ezzedine Al-Qassam Brigades said they had targeted the border crossing points of Sofa, Kessufim and Nahal Oz.
Palestinian witnesses said some 10 shells had been fired at Sofa.
A Palestinian emergency services official said a subsequent Israeli air strike Saturday on the neighbourhood of Zeitun, on Gaza City's outskirts, wounded five people.
Spokesman Adham Abu Selmiya said a child was among the injured in the attack, which was supposedly aimed at a Hamas security centre.
Witnesses said the Israelis also hit another target east of Khan Yunes, in the southern Gaza Strip, Saturday and the refugee camp of Deir El-Balah in the centre of the territory.
An Israeli military spokeswoman denied any air strikes but said ground forces backed by helicopters had fired on specific targets in the south of the Gaza Strip.
A statement from the office of Israel Foreign Minister Avigdor Lieberman said he had told the Israeli mission at the United Nations to raise the issue.
It noted the mortar fire came as Palestinian president Mahmoud Abbas, whose Fatah movement controls the West Bank, was stepping up efforts to effect a reconciliation with Hamas.
Saturday's barrage took the number of projectiles Israel says Gaza-based 'militants' have fired into its territory since the beginning of the year to past 100.
It carried out a massive 22-day bloody war against Gaza from December 2008 to January 2009, which killed 1,400 Palestinians, most of which were civilians, and 13 Israelis.
In January Gaza's main resistance factions agreed to observe a truce after weeks of increased rocket fire and rising tensions along the border which prompted a warning from Arab leaders that they were risking a major new Israeli invasion.
Gaza's Hamas rulers said they would ensure the "national consensus" truce was observed and deployed forces along the border zone.