Israel has begun work on a huge fortified breakwater in the Mediterranean sea to prevent infiltration from the Gaza Strip.
The "new and impenetrable" barrier being built off the Zikim beach, a few kilometres (miles) north of Gaza, is in effect a fortified breakwater topped with barbed wire, Israel's defence ministry said in a statement.
The ministry said the breakwater - the first of its kind in the world - was expected to be ready by the end of 2018.
"This is a unique obstacle that will effectively prevent the possibility of penetrating Israel by sea," Defence Minister Avigdor Lieberman said in a statement.
"This is another blow to Hamas, which will lose yet another strategic ability in which it invested vast amounts of money," he added, in reference to the Islamist movement that controls Gaza.
In the last Gaza war in 2014, Israeli forces killed four Hamas militants who had managed to infiltrate by sea.
Israel is meanwhile continuing the revamp of its border fence with the besieged enclave - reinforcements include a new massive underground barrier meant to neutralise the threat of tunnels.
Construction began as Gaza activists announced plans to breach the Israeli naval blockade of the territory, which has prevented any vessel travelling more than six nautical miles from the coast since 2007.
Few details were given on the plans, but organisers said the boat would depart on Tuesday at 11:00 am (0800 GMT) carrying patients needing medical care, students and job-seeking university graduates.Its intended destination was not announced.
The boat also brings "dreams of our people and their aspirations for freedom", Salah Abdul-Ati, the organiser, said in a press conference at Gaza City's port.
Organisers said it would be the first attempt to breach the naval blockade from the Gaza Strip side.
The plan comes ahead of the eighth anniversary on Thursday of a deadly raid on the Mavi Marmara, a Turkish-registered ship that was part of a six vessel flottilla that attempted to run the blockade in 2010.
No other details on the project were provided.
Israel has maintained a naval blockade of Gaza since 2007.
Boats off the strip are generally limited to six nautical miles offshore, and the Israeli navy regularly fires warning shots at Palestinians who breach it.
At least 119 Palestinians have been killed by Israeli fire in the Gaza Strip since mass protests and clashes broke out on March 30, according to figures from the Gazan health ministry.