Jerusalem ? Israel threatened “harsh and disproportionate” retaliation after Gaza militants fired at least 10 rockets and mortar shells across the border Sunday and warplanes later bombed the area where Hamas smuggles in weapons from Egypt through tunnels.

The flare-up raised the risk of growing violence in the days leading up to Israel’s parliamentary elections on Feb. 10.

Since an unwritten truce ended Israel’s offensive in Gaza two weeks ago, rocket and mortar fire from the Palestinian territory ruled by Hamas has increased steadily. Israeli retaliation, including brief ground incursions and bombings of rocket launchers and smuggling tunnels, is also intensifying.

“If there is shooting at residents of the south, there will be an Israeli response that will be harsh and disproportionate by its nature,” Prime Minister Ehud Olmert told his Cabinet.

Israel launched its three-week offensive with the aim of ending years of Hamas rocket fire at southern Israel. It left nearly 1,300 Palestinians dead, more than half of them civilians, according to Gaza officials. Thirteen Israelis were killed, including three civilians.

A late afternoon mortar barrage on the southern Israeli village of Nahal Oz, next to the Gaza border fence, wounded two soldiers and a civilian, the military and rescue services said. Earlier, a rocket landed near a kindergarten, police spokesman Micky Rosenfeld said.

Late Sunday, Palestinians reported huge explosions as Israeli warplanes dropped bombs on the Egypt-Gaza border area, where Hamas operates tunnels to smuggle in weapons, food and other goods, Palestinians said.

Israeli aircraft first flew over the area in southern Gaza setting off sonic booms. Residents said hundreds of people who work in the tunnels fled, then waited in the streets of the border city, Rafah, for the attacks to end so they could return.

The Israeli military said warplanes attacked six tunnels and also an unspecified Hamas post in northern Gaza. No casualties were reported from any of the bombings.

Hamas spokesman Taher Nunu said Olmert’s threat was an attempt by Israel to “find false pretexts to increase its aggression against the people” of Gaza.

Hamas has not taken responsibility for the new attacks, which have been claimed by smaller militant groups. But Israel says it holds Hamas, which has ruled Gaza since seizing power in June 2007, responsible for all attacks coming from there.