GAZA (Reuters) - Israeli tank shelling killed three members of the Palestinian militant group Islamic Jihad in the Gaza Strip on Sunday, medical officials said, after weeks of border protests that have drawn lethal army fire.

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Israel’s military confirmed the strike, saying it targeted an observation post in response to a bomb that had been placed next to the border fence overnight. Video issued on the military’s Twitter feed showed the bomb being detonated safely.

Islamic Jihad operates with a measure of independence from Hamas, the Islamist group that has controlled Gaza since 2007 and fought three wars against Israel.

Hostilities over the frontier have soared since Palestinians began mass-demonstrations on March 30, which Israel deems to be cover for attempts to breach the border fence.

At least 115 Palestinians have been killed and thousands hurt by army gunfire in the protests, drawing foreign censure.

Organizers said they would ramp up demonstrations on Tuesday with a flotilla of boats that would set off from Gaza in an attempt to break Israel’s maritime blockade of the enclave.

“Gaza has become a big, isolated prison, deprived of minimal rights, because of the unjust Israeli siege,” they said in a statement, referring to clampdowns by Israel and neighbor Egypt.

Israel has blunted the military capabilities of Hamas with a series of counter-measures: the Iron Dome air defense system against short-range rockets and a system for detecting and destroying cross-border guerrilla tunnels.

In the latest move, Israel’s Defence Ministry said on Sunday that work had started on a maritime wall that would block infiltration by seaborne Palestinian fighters from north Gaza.

The sea wall, due to be complete by the end of the year, entails three layers below and above the Mediterranean surface, and will employ fortified rock as well as barbed wire, the ministry said.

There have been no Israeli casualties along the Gaza frontier, but Israel has reported extensive damage to farmland on its side of the border from firebomb-bearing kites flown over by Palestinians.

To counter that threat, the Israeli military said it has mobilized private drone-racers as army reservists, who then try to ram into the kites with the remote-controlled aircraft.

“We’ll deal with the kites, too,” security cabinet minister Naftali Bennett told Israel Radio, when asked about the military’s actions around Gaza.

In Israel, the military announced the death on Saturday of a soldier who was injured during a raid in the occupied West Bank on Thursday when Palestinians dropped a stone slab on his head from a building. Hundreds attended his funeral in Jerusalem on Sunday.