International experts and aid organizations including the United Nations have repeatedly called the Israeli blockade a collective punishment against Gazans

The Israeli navy seized a Swedish-flagged sailboat attempting to breach a blockade of the Palestinian Gaza Strip Saturday, the military said.

The 12 passengers are mostly from Sweden but also from Germany, Britain, Spain, France and Canada. They are in custody and will be put on flights home, a spokeswoman for the Israeli Immigration Authority said.

The SY Freedom for Gaza was carrying mainly medical supplies and two of its passengers were journalists, said an organizer from a group named Ship to Gaza which organized the trip.

"Ship to Gaza demands that those who have been taken prisoner and the ship and its cargo are returned to the location where the ship was boarded and are allowed to continue their journey in international and Palestinian waters unmolested, in accordance with international law," the group said in a statement.

"The IDF (Israel Defence Forces) clarified to the ship's passengers that they are violating the legal naval blockade and that any humanitarian merchandise can be transferred to Gaza through the (Israeli) Port of Ashdod," an Israeli military statement said.

Similar attempts by activists to challenge the Israeli naval blockade of Gaza have been foiled before.

The most serious such incident was in 2010, when Israeli commandos raided a Turkish ship, the Mavi Marmara, that was leading a flotilla to Gaza. Ten activists aboard were killed, leading to a major diplomatic crisis between Israel and Turkey.

Israel has maintained a decade-long military blockade against the Palestinian territory which has resulted in humanitarian and economic crisis affecting the more than two million Palestinians packed into the Gaza Strip. International experts and aid organizations including the United Nations have repeatedly called the Israeli policy a collective punishment against Gazans for what Israel perceives as a threat by the Islamic Resistance group Hamas.

Also in recent months the Gaza strip and its population suffered yet another blow to their livelihood as the United States government decided to pull millions of dollars in aid to the UNRWA, the U.N. agency in charge of providing several sorts of aid to Palestinian refugees in the occupied territories West Bank and Gaza.