Eleven British pro-Palestinian activists have been detained at Tel Aviv's Ben Gurion Airport as Israeli authorities attempt to combat the so-called "flytilla".
Palestine Solidarity Campaign supporters left London on flights on Friday morning. One American was stopped from boarding a plane leaving Britain.
The activists said they intended to travel to Bethlehem in the West Bank. Israeli authorities had asked European airlines to prevent activists from flying.
As many as 200 people were stopped from boarding planes, including those hoping to travel from Paris, Berlin, and Geneva.
There have been chaotic scenes at Ben Gurion Airport as domestic pro-Palestinian campaigners, police, journalists and foreign activists converged on the main terminal.
Mick Napier of the Scottish Palestine Solidarity Campaign is co-ordinating the British arm of the initiative. Leaving Britain this morning, he said: "We are pleased that all British citizens have been able to board their flights, and are united in our commitment to appeal any attempt by Israel to deport us on arrival. If we are denied entry, the whole world will see that Israel's siege is not limited to Gaza, but surrounds the West Bank as well."
Israel increased security at airports in anticipation, with "flytilla" organisers predicting that as many as 600 activists would arrive in the country on Friday.
The campaign comes after pro-Palestinian activists' attempts to sail a flotilla from Greece to Gaza were stopped by Greek authorities.