An Irish aid vessel en route to Gaza is being tailed by two Israeli navy boats, according to activists on the ship.
There had been earlier reports that soldiers from the Israeli navy had boarded the ship, named the Rachel Corrie. But according to the Twitter account of the Cyprus-based Free Gaza Movement, those reports were incorrect.
The group, the major sponsor of the trip, said it has been on the phone with passengers, who say they are being followed by two Israeli ships but there has been no contact with the navy.
The ship, carrying 11 passengers, was reportedly 40 kilometres from Gaza. It is heading to Gaza in an attempt to break the blockade and deliver hundreds of tonnes of aid, including wheelchairs, medical supplies and cement.
Israel has vowed to stop the ship from breaching a three-year-old blockade on the Hamas-ruled Gaza Strip.
Those on board the Rachel Corrie have said they would not resist if Israeli soldiers tried to take over their vessel. They rejected an Israeli appeal to bring the ship to an Israeli port instead.
Earlier this week, hundreds of activists were taken into custody during a raid on a flotilla that was challenging the blockade. Israeli commandos stormed the boats in international water. Nine activists were killed.
Israeli Prime Minister Benjamin Netanyahu has reportedly instructed the military to act with sensitivity in preventing the Rachel Corrie from landing and avoid harming those on the ship.