An Irish aid ship has been forced to pull out of a flotilla attempting to break the Gaza blockade after it was damaged while docked in Turkey.
Human rights activists claim the lives of 20 Irish citizens were put at risk by a deliberate sabotage of the MV Saoirse, which they blamed on Israel.
Dr Fintan Lane, co-ordinator of Irish Ship to Gaza, said the damage to the propeller shaft was a potentially murderous act.
If pressure had been put on the shaft, which was weakened by a piece gouged out, it could have snapped, damaged the engine room and flooded the boat at sea, he said.
"This wasn't designed to stop the ship from leaving its berth. Instead it was intended that the fatal damage to the ship would occur while she was at sea and would have resulted in the deaths of several of those on board," he said.
"This was a potentially murderous act."
Six members of the Irish Ship to Gaza, including Dr Lane and former rugby player Trevor Hogan, plan to join an Italian ship, while seven other members will arrive back in Dublin airport tonight. Others hope to travel on other aid ships.
The damage is said to be identical to damage suffered by the Greek/Swedish ship, the Juliano, in recent days.
Dr Lane demanded that the Irish and European governments condemn the attacks despite Taoiseach Enda Kenny warning the Irish human rights activists yesterday against trying to break the blockade.
"Israel has no right to interdict the flotilla and even less right to carry out attacks against vessels in Greek and Turkish ports," he said.
Israel has not commented on the allegations.
About 10 ships are due to set sail this week from Greece. It is unclear if the damaged boats will cause a delay.
Israel imposed a naval blockade after Hamas militants overran the Palestinian territory in 2007.
It said it will not allow the flotilla to reach Gaza.
Last year, an Israeli raid on a similar flotilla killed nine activists on a Turkish vessel. Each side blamed the other for the violence.
Almost €130,000 was raised in Ireland to fund the humanitarian mission, which planned to take medication and sports equipment to Gaza.
Repairs to the vessel - which had been under constant watch since it arrived in the port of Gocek in early June - will cost an estimated €15,000.
Mark Hogan, brother of the former Leinster rugby star, said the group remained determined and confident about bringing an end to the immoral and illegal blockade on Gaza.
"They will not be deterred by the malicious and reckless sabotage on the MV Saoirse," he said.
"This outrageous attack has instead reinforced their desire to complete their mission and sail to Gaza with their cargo of humanitarian aid."
Hogan described activists in Freedom Flotilla II as a brave collection of ordinary individuals reaching out in solidarity with a society which has been systemically dehumanised and humiliated.
He revealed it was his brother's ambition to see young Palestinians spinning rugby balls to each other.
"I urge the Irish Government not to stand idly by any further but to intervene and contact the Israeli government and ensure the safe passage of Freedom Flotilla II," he added.