Israel launched retaliatory air strikes on the Gaza Strip on Thursday hours after its top soldier warned troops to be prepared for possible "wider action" on the enclave's volatile border.

An Israeli military spokeswoman said the strikes were aimed at three separate targets, two of which Gaza militants confirmed were sites they used for training. No casualties were reported.

The air strikes were launched overnight after a mortar fired by Gaza militants wounded an Israeli man at a farm.

"The situation on the Gaza Strip border is fragile these days," Israeli armed forces chief General Gaby Ashekenazi told troops based near the Gaza border, according to the Maariv daily.

Ashekenazi cited a large number of explosive devices on the border and rising activity against Israel at the northern edge of Gaza, predicting more incidents.

"We may need to be prepared for wider action. The next round will be big and it needs to end in a way that leaves no doubt who won. We are significantly stronger than the other side," the commander said, according to Maariv.

Militants in the enclave ruled by the Islamist Hamas faction have fired some 200 rockets and mortars at Israel this year, the Israeli army says.

They fired about five mortar rounds late on Wednesday and fragments from one wounded a man. He was taken by helicopter to hospital in Beersheba, but his injuries were not life-threatening, the army spokeswoman said.

He was the first casualty since March, when a Thai farm  labourer was killed by a mortar shell.

Heavy blasts

Israel usually responds to the attacks with tank fire or air strikes against militant targets or the tunnels they use to smuggle goods and arms into the territory from Egypt.

On Thursday, Israeli missiles hit a training field of the Hamas armed wing, causing damage to several nearby houses and a primary school of 700 students, witnesses said.

All the windows in the three floors of our houses were smashed. Our bedroom door was blown in," said one woman. "Every time they hit the training camp we get hurt," her son said.

Israel holds Hamas responsible for all mortar and rocket attacks, regardless of which of Gaza's militant factions fires them. Thursday's attack was claimed by the Popular Resistance Committees and the Popular Front for the Liberation of Palestine, who said their fighters had confronted Israeli army forces that penetrated the border fence with the enclave.

Israel ended 38 years of Gaza occupation in 2005 but it began blockading the strip in 2007 after Hamas Islamists hostile to the Jewish state seized power from Palestinians prepared to negotiate peace with Israel.

Palestinians and some United Nations officials say Israel's occupation can only truly end when it gives up control of Gaza's borders, coast and airspace. – Reuters