Jerusalem (CNN) -- Israeli sailors boarded two aid ships headed to the Palestinian territory of Gaza on Friday, the Israeli military said.
While no resistance was reported, activists criticized the Israeli action as "illegal" and vowed that activists "will keep coming, wave after wave" to try to deliver aid to Palestinians in Gaza.
Activists on board the "Freedom Waves to Gaza" mini-flotilla were "attempting to break the maritime security blockade that is in place in accordance with international law," the Israeli military said, and were refusing to heed their calls to turn back.
"The boarding was carried out in line with directives from the Israeli government and after all attempts to prevent the vessels from reaching the Gaza Strip were made, but to no avail," the military said.
"The boarding was carried out following numerous calls to the activists on board and during different points at sea. Following their unwillingness to cooperate, and after ignoring calls to divert to the port of Ashdod, the decision was made to board the vessels and lead them there."
Sailors "took every precaution necessary to ensure the safety of the activists on board the vessels as well as themselves," the Israel Defense Forces said.
Activists will be handed over to Israeli police and immigration authorities, the military said.
According to the activist organizers, this mission was the eleventh attempt to run Israel's blockade of Gaza by sea. Five missions arrived safely in Gaza between August and December 2008, with the rest intercepted by Israel.
The activists said Friday that "ground support crews lost contact with two ships, the Saoirse of Ireland and the Tahrir of Canada." It said there are 27 civilian passengers. The boats are carrying medical supplies and letters of support for people in Gaza.
The activists said the navy interrogated people on the Tahrir around 7:30 a.m., when it was about 48 nautical miles from the Gaza coast. Thirteen minutes later, ground support crews lost contact with two ships.
Asked by the Israeli Navy for their destination, Canadian activist Ehab Lotayef replied, "The conscience of humanity," the activists' said in a statement.
When they repeated the question, asking for final destination, Lotayef said, "The betterment of mankind."
Kit Kittredge, an American traveling with the Tahrir, said Israelis made contact with the group and told them to change their radio channel. Kittredge said the group declined to do so.
Late Thursday, two Israeli navy ships shadowed the ships before pulling back, the group said.
The activists said the ships had been "illegally boarded."
"It's clear that 27 civilians on two small boats, carrying only medicine, constituted no security threat to the Israeli state, and that the determination to keep them out is only a furtherance of Israel's policy of collective punishment, a crime against humanity," said Huwaida Arraf, spokeswoman for Freedom Waves to Gaza.
"Despite this Israeli aggression, we will keep coming, wave after wave, by air, sea, and land, to challenge Israel's illegal policies towards Gaza and all of Palestine," Arraf said. "Our movement will not stop or be stopped until Palestine is free."
Jane Hirschmann, U.S. coordinator for the Freedom Waves to Gaza flotilla, said, "Had the passengers been permitted to proceed to Gaza rather than being stopped on the high seas by armed force, there would have been no threat to their safety. The IDF's statement is like the mugger promising to escort his victim home safely."
Ann Wright, one of the organizers of the Freedom Flotilla that attempted to sail to Gaza last June, said,"It's a little hard to imagine how 27 unarmed civilians on two small boats carrying medicine and letters threaten Israel's security. Israel is simply determined to maintain its policy of collective punishment against the 1.6 million civilians in Gaza. This is a crime against humanity and violation of international law. Despite Israel's consistent use of military force against nonviolent protests and demonstrations, activists around the world will continue to challenge the occupation of Palestine and the blockade and Gaza."
Passengers on the boats are from Canada, Ireland, the United States, Australia, and the Palestinian territories, the activists say.
The flotillas have sparked international controversy.
In 2010, an Israeli raid on one flotilla ship, the Mavi Marmara, resulted in nine Turkish activists being killed, a development that led to the deterioration of relations between Israel and Turkey, once close allies. Israel was roundly criticized by many over the deaths.
A U.N. report criticized Israel for its use of excessive force in the incident but described the blockade -- which activists call illegal -- as a "legitimate security measure."
Israel says it is concerned about the smuggling of arms to Gaza militants intent on attacking the Jewish state. Gaza is controlled by the anti-Israel Hamas militant group, regarded as a terrorist group by the United States and Israel,
But activists say Israeli embargoes of goods into Gaza from land and sea are collective punishment of civilians in what is a tiny and densely populated strip of land along the Mediterranean coast.
Israel has said any organization or state that wants to give humanitarian aid to Gaza can do so in coordination with Israeli authorities via existing land crossings into the Palestinian territory.
CNN's Kareem Khadder and Nicky Robertson contributed to this report.