A US-based pro-Palestinian movement on Tuesday accused the Israeli navy of "abducting" 21 pro-Palestinian activists aboard an aid boat heading for the besieged Gaza port.

Israeli forces "attacked and boarded the Free Gaza Movement boat, the Spirit of Humanity, abducting 21 human rights workers from 11 countries, including Noble laureate Mairead Maguire and former US Congresswoman Cynthia McKinney," said a statement from the Free Gaza Movement.

The organization termed it as "an outrageous violation of international law," since their boat was about 21 miles away off the coast of Gaza, not in Israeli waters and they were on a human rights mission to the Gaza Strip.

"President Obama just told Israel to let in humanitarian and reconstruction supplies," McKinney said. "That's exactly what we tried to do."

"We're asking the international community to demand our release so we can resume our journey," she said.

Fellow passenger Maguire, winner of a Noble Peace Prize for her work in Northern Ireland, said the aid they were carrying is "a symbol of hope" for the people of Gaza, foreshowing that the sea route would open for them, and they would be able to transport their own materials to start reconstruction of the schools, hospitals and thousands of homes destroyed during the Israeli operation "Cast Lead."

The vessel, with three tons of medical aid, toys and rehabilitation and reconstruction kits on board, left the Cypriot port of Larnaca on Monday morning. It first sailed southward in the direction of Egypt, and then turned southeast, heading for Gaza port, when the Israeli navy stopped it.

The movement last year successfully challenged the Israeli embargo on Hamas-controlled Gaza five times, sailing the first international ships to Gaza port since 1967. But their attempts earlier this year failed, either due to technical problems or Israeli blockades.

International donors have pledged more than 4 billion US dollars in aid for Gaza in the aftermath of the Israeli military operation, but little humanitarian aid and no reconstruction supplies have been allowed in.