Solidarity activists have called on Tel Aviv to 'call off their attack dogs' after commandos boarded their converted ferry and threatened to arrest them unless they turned back from Gaza.
The Spirit of Humanity, which left Larnaca on Monday with three tons of medical supplies, toys and building materials, was scheduled to arrive at the besieged territory this afternoon.
But at 1.30am today, when the small civilian boat was 45 miles from Gaza port, five Israeli warships surrounded it and soldiers reportedly threatened to open fire if they did not turn around.
The activists - including former US Congresswoman Cynthia McKinney, Nobel Peace Prize laureate Mairead Corrigan Maguire and others from Britain, Ireland, Bahrain and Jamaica - refused to be intimidated and pressed on.
The Israeli forces then began jamming their instrumentation, blocking their GPS, radar and navigation systems.
The US-based Free Gaza Movement (FGM) which organised the humanitarian mission observed that, by threatening the welfare and safety of the civilian ship, Israel had directly violated international maritime law.
With just 25 miles to go, commandos boarded the Spirit of Humanity and threatened to detain the solidarity campaigners unless they called off their humanitarian mission.
Ms McKinney demanded that the Israeli government 'call off their attack dogs.
'We are unarmed civilians aboard an unarmed boat delivering medical and reconstruction aid to other human beings in Gaza - why in God's name would Israel want to attack us?'
FGM chairwoman Huwaida Arraf stressed that the solidarity campaigners 'do not seek a confrontation.
'All we want is to reach Gaza - we want to visit our friends and deliver our cargo of medical supplies, children's toys and reconstruction materials.'
Ms Arraf vowed that, even if the activists were stopped from delivering their cargo this time, they would 'come to Gaza again and again until this brutal siege is broken,' inviting 'the good people of the world to join us.'
Israeli foreign ministry spokesman Yigal Palmor denied that Israeli forces had threatened to shoot at the Spirit of Humanity, insisting 'no such threats' had been made.
It is unclear if Israeli authorities will allow the ship to continue on to Gaza, but an FGM spokeswoman conceded yesterday afternoon that this was looking increasingly unlikely.