Israeli naval forces on Tuesday boarded a French yacht that was heading for the Gaza Strip in defiance of its naval blockade and began towing the vessel to shore, a military spokeswoman said.

"The Israeli navy has boarded the ship," a military spokeswoman told AFP saying the operation to board the MV Dignite/Al Karama had been conducted peacefully and that the ship was being towed towards the Israeli port of Ashdod.

The ship, which is carrying 16 people, most of them French activists, was commandeered by the navy shortly after Israel army Chief of Staff Lieutenant General Benny Gantz authorised the move, she said.

Israel has consistently vowed to block any vessels from reaching Gaza by sea in defiance of its naval blockade which was first imposed in 2006 after militants there snatched an Israeli soldier.

"After all diplomatic channels had been exhausted and continuous calls to the vessel had been ignored, IDF Navy soldiers boarded the Al Karama in an effort to stop it from breaking the maritime security blockade on the Gaza Strip," an army statement said.

 The navy first approached the boat some five hours earlier and began a dialogue with those on board who had insisted they would pursue their course for Gaza.

"Upon expressing their unwillingness to arrive at the Ashdod port, it was unequivocally necessary to board the vessel and lead it there," the military statement said.

"The soldiers operated in line with procedures and took every precaution necessary... (to) avoid causing harm to the activists on-board while ensuring the safety of the soldiers."

The French-flagged yacht had first been approached in international waters by at least three Israeli navy boats at 0630 GMT when it was some 40 nautical miles off Gaza, organisers said.

Shortly afterwards, all communications were cut, organisers said in a statement, urging the the French government "to take its responsibilities and to protect the passengers, and to call on Israel not resort to violence."