(Adds new air strikes, army comment, details)

By Nidal al-Mughrabi

GAZA, Feb 1 (Reuters) - Israel launched a series of air strikes in the Gaza Strip on Sunday, targeting a Hamas security complex and tunnels used to smuggle weapons after vowing a "disproportionate" response to cross-border fire.

The aircraft carried out half a dozen strikes after three Israelis were injured by a mortar salvo, including two soldiers and the first Israeli civilian hurt since a Jan. 18 truce ended Israel's 22-day offensive in the coastal enclave.

There were no reported casualties in the air attacks. Five of the strikes targeted tunnels along Gaza's border with Egypt, used to smuggle weapons into the coastal enclave, in a zone known as the Philadelphi corridor.

A further Israeli attack was on a security headquarters in a village in central Gaza that residents said had been vacated after Israel telephoned warnings to Palestinians to leave buildings that housed any weapons.

An Israeli military statement said that "in response to rocket and mortar fire today, the air force has attacked a number of targets in the (Gaza) Strip, including six tunnels and a Hamas position." Hamas said five tunnels had been bombed.

Egypt, with U.S. backing, has been trying to broker a long-term ceasefire that would end Hamas weapons smuggling into Gaza and also lead to a reopening of Gaza border crossings, one of Hamas's main demands.

Israel's blockade of Gaza, since Hamas Islamists seized the coastal territory from Western-back Palestinian President Mahmoud Abbas in 2007, has led to shortages of crucial supplies for many of the 1.5 million Palestinians living there.

Israel's renewed air strikes came as its leaders took a hard line against rocket fire from Gaza ahead of a Feb. 10 national election, which opinion polls predict right-wing leader Benjamin Netanyahu, who favours a tougher stance toward Hamas, will win.

About a dozen rockets and mortar bombs were fired from Gaza on Sunday, the Israeli military said.

A wing of al-Aqsa Martyrs Brigades, a group belonging to Abbas's Fatah faction, said it fired some of the rockets, but not all were claimed.

THREATS OF A "HARSH" RESPONSE

"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, who is not an election candidate, said at the weekly cabinet meeting.

"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.

Israeli radios quoted Foreign Minister Tzipi Livni, a candidate for prime minister as head of the centrist Kadima party, as saying Israel would mount a new offensive in Gaza if necessary to halt rocket fire from Gaza.

Olmert is not running, as he quit during a corruption probe in September and has stayed on as caretaker premier.

A spokesman for the Hamas government in the Gaza Strip condemned what he described as Olmert's "aggressive statement".

But the spokesman, Taher al-Nono, also urged all Palestinian factions to "respect the national consensus" on the ceasefire the Islamist group declared two weeks ago after Israel announced it was halting the Gaza offensive.

Israel was criticised internationally for the deaths, according to the Hamas-run Health Ministry in Gaza, of more than 1,300 Palestinians, including at least 700 civilians in the offensive it launched on Dec. 27.

Critics said Israel had responded disproportionately, in its air and ground offensive in heavily populated areas, to cross-border rocket attacks over eight years that killed 18 people. Ten Israeli soldiers and three civilians were killed in the Gaza campaign.

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

Since the two-week-old truce, in addition to Sunday's injuries, an Israeli soldier was killed and three others were wounded when a bomb exploded next to their patrol. Israeli air strikes have killed three Palestinians and wounded 10. (Additional reporting by Allyn Fisher-Ilan, Jeffrey Heller, Adam Entous, Ari Rabinovitch and Dan Williams in Jerusalem; Editing by Charles Dick)

AlertNet news is provided by