The Israeli navy on Friday boarded two international ships carrying pro-Palestinian activists who were trying to break the blockade on the Hamas-run Gaza Strip, a military statement said.

The Irish-flagged Saoirse ("Freedom") and the Canadian ship Tahrir (Arabic for "Liberation") were intercepted by naval commandos in international waters off the Gaza coast, ending the latest attempt to reach the coastal enclave.

An Israeli security source said there were "no injuries" during the boarding process which occurred just minutes before the start of the Jewish sabbath.

"A short while ago, Israel navy soldiers boarded the vessels which were en route to the Gaza Strip, attempting to break the maritime security blockade that is in place in accordance with international law," the statement said.

The move came after the two ships refused to heed calls to change course, prompting military Chief of Staff Benny Gantz to order their interception.

"The IDF Chief of Staff ordered the navy to board the vessels should they refuse our radio requests," the military spokesman's unit tweeted, using the identifying hashtag "provocatilla."

Moves to board the ship came three hours after the navy had first made radio contact with the two vessels, warning them not to continue into naval territory which was under "a maritime security blockade in accordance with international law."

Dublin-based organisers of the Irish boat said they had been contacted by those on board just before 1:00 pm (1100 GMT) to say they were being "rapidly" approached by two Israeli warships, with first radio contact made some 15 minutes later.

"The Israel navy advised the vessels that they may turn back at any point," the military said, adding: "The activists refused to cooperate."

Shortly afterwards, organisers said they had lost contact with the two boats.

The last time a boat tried to reach Gaza was in July, when a French-flagged yacht, the last remaining boat of an earlier flotilla, was intercepted by the Israeli navy some 40 nautical miles off the coast.

The Irish boat is carrying 15 passengers and crew members. The Canadian boat has 12 people on board, five of them journalists, and has a cargo of $30,000 (22,000 euros) worth of medical aid and letters of solidarity, organisers said.

Denis Kosseim, a Montreal-based spokesman for the Canadian Boat to Gaza campaign had earlier told AFP the passengers and crew would not put up a fight if Israel moved to intercept the boards.

"Those on board have been instructed not to put up any resistance to the Israeli navy when it tries to intercept them," he said.

"Everyone has signed a document in which they pledged not to put up any resistance should they be boarded by Israel," he added.

On Thursday evening, Israeli warships came within six nautical miles of the two vessels, sparking unfounded fears they might board the ships overnight.

Activists organised a major attempt to break the Israeli blockade in May 2010, when six ships led by the Turkish Mavi Marmara tried to reach Gaza.

Israeli troops stormed the Marmara, killing nine Turkish activists and sparking a diplomatic crisis with Ankara, which expelled the Israeli ambassador and has cut military ties with the Jewish state.

Earlier this year, a second flotilla tried to reach Gaza, but several ships were sabotaged -- which activists blamed on Israel. Only the French-flagged yacht, the Dignity, was able to attempt the last leg of the journey but was stopped by the navy and those on board were deported.

Israel says its blockade is necessary to prevent weapons from entering the coastal territory, which is run by the Islamist Hamas movement.

Two months ago, a UN report on the flotilla raid accused the Jewish state of acting with "excessive force" but found that its naval blockade on the coastal territory was legal.