Two Palestinians were hurt, one critically, in an Israeli air strike on Gaza City on Sunday, which the military said had targeted a senior Islamic Jihad militant.

The strike, the third in 12 hours, came a day after militants fired another rocket at southern Israel, prompting a sharp warning from Israeli Prime Minister Benjamin Netanyahu.

"We are determined to maintain quiet in the south. We will do so by a policy of preventive action and strong reaction against those who try to harm us or who harm us," he told ministers at the weekly cabinet meeting.

"I suggest that Hamas take our policy into account," he said, referring to the Islamist movement which rules Gaza.

Gaza emergency services spokesman Ashraf al-Qudra said the strike had hit a motorcycle in the northern neighbourhood of Saftawi, leaving its rider, a 22-year-old man, in critical condition.

A 12-year-old boy who was standing nearby suffered moderate wounds in the raid, he told AFP.

"I was there and saw the strike, a motorcycle burst into flames and a car drove away," said witness Saad al-Dabbur, adding that he initially thought there had been a road accident until he saw a donkey lying dead on the ground.

Shortly afterwards, the Israeli army confirmed the strike, saying it targeted a "senior operative" in the radical Islamic Jihad movement, identified as Ahmad Saad and accused of planning an imminent attack on Israel.

"The IDF (Israel Defence Forces) successfully targeted a terrorist operative involved in recent attacks against Israel and was planning further attacks in the coming days," it said in a statement.

"Saad is personally responsible for the launching of five rockets towards Ashkelon on January 16, 2014 which were intercepted by the Iron Dome missile defence system.

"The IDF operated in order to eliminate an imminent threat to the lives of Israeli civilians," said the army.

There was no confirmation from Gaza that the wounded man was Saad or that he belonged to Islamic Jihad, with sources in the radical movement also refusing to comment on the strike.

The morning strike followed early morning raids which struck training grounds used by the militant wing of the ruling Hamas movement: one in Nusseirat refugee camp in central Gaza; and a second in the south near Khan Yunis, officials said.

No-one was hurt in the raids which followed rocket fire on Israel on Saturday, which also caused no injuries or damage.

On January 8, an Islamic Jihad militant was died near Gaza City in what medics and family said was an Israeli drone strike, but the army denied any involvement.

Over the last month, tensions have risen in and around Gaza after a year of relative calm, with four Palestinians and an Israeli killed since December 20.

Since January 1, eight rockets fired from Gaza have landed in Israel with another five intercepted by Iron Dome last Thursday.