The Global Sumud Flotilla, an international aid initiative to deliver vital supplies to Gaza, said on Wednesday that one of its boats was attacked by a drone at a Tunisian port, the second such strike in two days.
The GSF, which is seeking to break Israel's naval blockade and deliver humanitarian aid to war-torn Gaza using civilian boats, said in a statement that all passengers and crew were unharmed.
GSF reported the first attack on Tuesday, saying one of its vessels had been struck by a drone in Tunisian waters at the Sidi Bou Said port, reports Tunisian authorities said were false.
One of the flotilla's organisers accused Israel of carrying out the attack.
"Israel continues to breach international law and terrorise us. We will sail to break the blockade on Gaza no matter what they do," Saif Abukeshek, a member of the GSF steering committee, told Reuters.
The Israeli military did not immediately respond to a request for comment.
The flotilla posted a video on Instagram of the alleged attack, showing a luminous object hitting the boat and fire erupting on board. Reuters was not immediately able to verify the video.
Following the strike, hundreds gathered near the port, where the flotilla's boats were located at the time of the incident, waving Palestinian flags and chanting slogans against Israel and the United States.
The group said that the British-flagged Alma sustained fire damage to its top deck and an investigation was underway.
Several ambulances rushed to the port, while a Reuters witness reported coastguard boats near the Alma.
The flotilla is supported by delegations from 44 countries, including Swedish activist Greta Thunberg and Portuguese left-wing politician Mariana Mortagua.
By Tarek Amara and Enas Alashray