RT's Nadezhda Kevorkova who is on board the Marianne, the flotilla’s flagship, said by phone that a military helicopter had been flying above the flotilla as well as an unknown military plane “flying very low above the water” near the activists’ vessels.

The Freedom Flotilla Coalition lost contact with the flagship of the flotilla at 10:57pm GMT, the organization said. The vessel was some 100 nautical miles from its destination when it happened.

The Israeli navy has engaged the vessel, boarded and searched it, the Israeli Defense Forces' spokesman Peter Lerner confirmed. He said the Marianne is now being escorted to Ashdod Port after ignoring "repeated appeals to change course."

Earlier, the Coalition confirmed that three vessels which are part of the flotilla turned back to their ports of origin, as was part of the original plan.

“The three sailing boats accompanying and supporting the “Marianne” (“Rachel”, “Vittorio” and “Juliano II”) are changing their course and will be heading back to their ports of origin,” it announced.

The Israeli government ordered the navy to “redirect” the vessel only after “exhausting all diplomatic channels,” according to the IDF. After the Marianne crew refused to change the course, the naval forces “visited and searched the vessel” and “reported that use of force was unnecessary, and that the process was uneventful.”

“The vessel is currently being escorted to Ashdod Port and is expected to arrive within 12-24 hours,” the statement adds.

Israel is maintaining its naval blockade of Gaza according to international law, as confirmed by the US Secretary General, said Israeli Foreign Affairs deputy spokesman, Oren Rozenblat, answering RT’s question about why Israel is deploying the military against civilian ships.

Activists aboard the intercepted ship are “fine and on their way to Israel,” said Rozenblat, stressing that maybe he will greet them personally tonight. The activists will be expelled from Israel as soon as possible, he added.

“There is no humanitarian crisis in Gaza whatsoever,” claimed the official, commenting on the Israeli prime minister’s office sarcastically proposing the flotilla head for Syria instead.

However, the European activists against Gaza siege don’t agree with the Israeli official. Rami Abdo, one of the campaigners, says ‘the situation on the ground is dire.’

Rozenblat also asserted there is no siege in Gaza. “We’ve hundreds of truckloads of goods coming to Gaza every day,” he said, adding that Israel could “send even more” goods, but that depends on the Gazans’ spending power. “There is no limitation from our side.”

However, the organizers of the flotilla have reasons to believe that the engagement was not as uneventful and non-violent as the navy claims, and that some people on board “might be hurt.”

“We could not contact the boat or anyone on the boat in the last couple of hours before capture,” a representative of the Freedom Flotilla III media team told RT by phone. “We have no reason yet to believe that the capture was [as] uneventful as the IDF claimed, because the last time they said [that] in 2012, people were tasered and beaten with clubs.”

The coalition expected Tel-Aviv to make every effort to stop the third Freedom Flotilla, but still hoped that “at some point a more reasonable voice will prevail in the Israeli government.”

Meanwhile, Israeli PM Benjamin Netanyahu has praised the navy personnel “for their determined and efficient” actions that allowed for the maintenance of the the blockade.

“This flotilla is nothing but a demonstration of hypocrisy and lies that is only assisting the Hamas terrorist organization and ignores all of the horrors in our region,” Netanyahu said. “We are not prepared to accept the entry of war materiel [in] to the terrorist organizations in Gaza as has been done by sea in the past.”

“Israel is the only democracy that defends itself in accordance with international law,” Netanyahu was cited as saying in an issued statement.

“Preventing entry by sea was done in accordance with international law and even received backing from a committee of the UN Secretary General,” the Israeli PM claimed.

The four vessels which departed from various ports in Greece on Saturday attempted to break the eight-year long Palestinian blockade, a news release on the campaign’s official webpage said. This time, some 70 people were on board, including former Tunisian President Moncef Marzouki and Spanish MEP Ana Maria Miranda Paza.

Israeli officials said on Sunday they would not allow the boats to reach the shores of Gaza.

"The Foreign Ministry and all other relevant bodies, mostly the IDF (Israel Defense Forces) and the Prime Minister’s Office, are fully prepared for the arrival of the flotilla. We are ready for every possible scenario," the ministry's spokesperson Emmanuel Nahshon said on Sunday, as quoted by The Times of Israel.

"It won’t reach Gaza," he announced. "The State of Israel won’t let that happen," the official said, adding that the organizers of the flotilla have themselves declared their aim to be the breakage of Israel's naval blockade of Gaza, which Jerusalem says "is legal according to international law."

In 2011, a report by a UN investigative committee implied that Israel has the right to stop Gaza-bound vessels, The Times of Israel reported. On Wednesday, UN Secretary-General Ban Ki-moon said he believed "a flotilla will not help to address the dire situation in Gaza," but urged Israel to "lift all closures, with due consideration of Israel's legitimate security concerns."

While Israel says the blockade is intended to prevent Hamas from getting weapons and other materials that could potentially be used to attack it, the flotilla allegedly only had humanitarian aid set to be delivered to the people of Gaza.

There are other "acceptable and accessible" ways for Palestinians-addressed help in Gaza, Nahshon said, adding that "if they [the flotilla] want to make a statement to break the blockade, we won't allow that."

A number of politicians and activists in Israel do not support such uncompromising position, arguing that the flotilla is peaceful and poses no danger to the country's security. Sending in troops could further seal Israel's image as an "aggressor," The Times of Israel said, citing a former Knesset member and prominent far-left activist Uri Avnery.

In 2010, a similar attempt to break the blockade with the "Freedom Flotilla" ended in bloodshed. Israeli troops then boarded a Gaza-bound vessel in international waters. Nine pro-Palestinian activists made a stand against the military with rods and knives, with the clashes having resulted in the deaths of the flotilla team members.