JERUSALEM, Feb 1 (Reuters) - Israeli Prime Minister Ehud Olmert threatened on Sunday a "disproportionate response" to the continued firing of rockets into Israel from the Hamas-ruled Gaza Strip.

There have been sporadic rocket attacks by militants on southern Israeli communities and several Israeli air strikes in the Gaza Strip since a truce came into effect on Jan. 18 following a 22-day Israeli offensive in the territory.

At least two rockets struck southern Israel on Sunday, causing no damage or casualties. A wing of al-Aqsa Martyrs Brigades, a group belonging to Palestinian President Mahmoud Abbas's Fatah faction, claimed responsibility.

"The government's position was from the outset that if there is shooting at the residents of the south, there will be a harsh Israeli response that will be disproportionate," Olmert said at the weekly cabinet meeting after the latest rocket salvo.

"We will act according to new rules which will ensure that we will not be drawn into a war of incessant shooting on the southern border, which would deprive the residents of the south of a normal life," he said, without elaborating.

Israel was criticised for the deaths, according to the Hamas-run Health Ministry in Gaza, of more than 1,300 Palestinians, including at least 700 civilians, during the war.

Critics said Israel had responded disproportionately, in its air and ground offensive in heavily populated areas, to cross-border rocket attacks over the previous eight years that killed 18 people.

Israel said Hamas militants bore responsibility for civilian deaths in Gaza by operating inside its towns and refugee camps.

During the Gaza campaign, 10 Israeli soldiers and three civilians were killed.

TOUGH TALK

Olmert's comments were echoed by Foreign Minister Tzipi Livni, a candidate for prime minister in Israel's Feb. 10 election. Olmert, who quit in a corruption scandal in September but stayed on as caretaker prime minister, is not running.

"Israel will respond," said Livni, who replaced Olmert as head of the ruling, centrist Kadima party. "This is my position. It was clear before, during and after the operation, and this is how I will conduct myself as prime minister."

Opinion polls in the final stretch of an election campaign dominated by security issues and promises by candidates to keep Hamas at bay, suggest the right-wing Likud party of former Prime Minister Benjamin Netanyahu will win the most votes.

Defence Minister Ehud Barak, whose Labour Party is running in fourth place in some polls behind Likud, Kadima and the ultranationalist Yisrael Beitenu party, said Israel would respond "in the proper manner" to attacks from the Gaza Strip.

"And I say this to us all: act judiciously and responsibly at this time. This is, after all, an election season," Barak said in broadcast remarks at the cabinet session.

"We are seeing a procession of chitchat from people -- some of whom never held a weapon in their hand, never made a real decision, and are now vying for headlines without understanding the conditions, the methods, the factors, the manner in which action should be taken," said Barak, a former general. (Additional reporting by Dan Williams, Editing by Elizabeth Piper)