Israel's military said early on Sunday it launched strikes against "militant targets" in the Gaza Strip, a day after rockets were fired from the Hamas-ruled territory.

Video filmed in Khan Younis, southern Gaza Strip, showed three huge explosions and fighter jets could be heard flying overhead. There was no immediate confirmation on possible casualties.

The Israeli military said the attacks targeted a rocket manufacturing facility and a military post for Hamas. It also blamed Hamas for any violence emanating from the territory it controls.

The airstrikes come as retaliation for two rockets fired from Gaza on Saturday which landed in the Mediterranean Sea off central Israel.

It was not clear whether the rockets were meant to hit Israel, but Gaza-based militant groups often test-fire missiles toward the sea. There were no reports of casualties from Saturday's rocket launches.

Apart from a single incident in September, there has been no cross-border rocket fire since a cease-fire ended an 11-day war between Israel and Hamas in May.

The cease-fire, brokered by Egypt and other mediators, has been fragile. Hamas says Israel did not take serious steps to ease the blockade it imposed on Gaza with Egypt's help when the Islamic movement seized control of the coastal enclave in 2007.

Concern over 'critical' prisoner

Tension are also high as other groups like the smaller but more hardline Islamic Jihad threaten military escalation if Israel doesn't end the administrative detention of a Palestinian prisoner who has been on a hunger strike for over 140 days.

The prisoner, Hisham Abu Hawash, a 40-year-old member of the Islamic Jihad militant movement, began refusing food in August to protest Israel holding him without charges or trial.

The married father of five from Dura in the south of the Israeli-occupied West Bank was being held under administrative detention, a practice of arresting suspects for renewable six-month terms without allowing them to view the charges or evidence against them.

“His condition is difficult and complex,” Liad Aviel, spokesman of the Shamir Medical Centre in central Israel where Abu Hawash is being held, told AFP.

The International Committee of the Red Cross said medical teams that visited Abu Hawash had found him “in critical condition requiring expert clinical monitoring”.

On Wednesday, Palestinian fighters in Gaza shot and lightly wounded an Israeli civilian near the security fence and Israel responded with tank fire targeting multiple Hamas sites in the first exchange of fire in months.