Seven Irish people are among the 175 activists arrested by Israeli authorities, after 20 ships from an aid-laden flotilla bound for Gaza were intercepted.
"Approximately 175 activists from more than 20 boats... are now making their way peacefully to Israel," Israel's foreign ministry said in a statement, including a video of the activists on board an Israeli navy ship.
The organisers of the flotilla said Israeli forces intercepted the aid ships in international waters near Greece, decrying the move as an "escalation of Israel's impunity".
The sister of President Catherine Connolly, Margaret Connolly, is on board one of the vessels that is part of the flotilla.
It is understood that the ship she is on was not intercepted by Israeli forces and is still sailing towards Greece.
Caoimhe Butterly, who is an Irish activist on board an independent observer vessel following the flotillas, said the ages of those detained range from mid-20s to a mariner who is 76 years old.
Speaking on RTÉ's Morning Ireland, she said she has received no updates.
However, she said one of the main vessels in the military action was a large naval vessel, and perhaps people were transferred to that, but they could still be on their sailboats.
"We were over 1,000 miles from Gazan territory or waters, so although those on board had prepared themselves for the possibility of illegal interception it was certainly not something we were expecting to begin, so close to Greece, to Crete and in clear violation of international law, yet again."
Ms Butterly was within the fleet when the interceptions happened before creating some distance.
However, she said based on what she could observe and radio communications, the interception began with Israeli commandos going "boat by boat, taking control of the boats and placing those on board under detention which, under international law, constitutes illegal detention in waters that are not under the jurisdiction of the Israeli army".
She added that this could translate to a possibility of illegal kidnapping on the high seas.
A second flotilla carrying humanitarian aid to Palestinians in Gaza sailed from the Spanish port of Barcelona on 12 April, aiming to try to break the Israeli blockade.
Watch: Irish woman describes interception of Gaza aid flotilla by Israel off Greece
The vessels were seized by Israel hundreds of miles from Gaza, said the organisers, Global Sumud Flotilla.
"This is piracy," the group said in a statement.
No state had the right to claim, police, or occupy international waters, but Israel had done that, extending its control outward to occupy the Mediterranean Sea off the coast of Europe, it added.
"This is the unlawful seizure of human beings on the open sea near Crete, an assertion that Israel can operate with total impunity, far beyond its own borders, with no consequences."
Israel controls all entry points to Gaza and has been accused by the United Nations and foreign NGOs of strangling the flow of goods into the territory, causing shortages since the start of its war in Gaza in October 2023.
Israel's UN envoy Danny Danon said the flotilla "was stopped before reaching our area".
Israel's military halted a previous flotilla assembled by the same organisation last October in an attempt to reach blockaded Gaza, arresting more than 450 participants.
Palestinians and international aid bodies say supplies reaching the territory are insufficient, despite a ceasefire reached in October that included guarantees of increased aid.
Liam Cunningham, an actor who starred in the Game of Thrones television series who is supporting the flotilla but not taking part, said: "Every kilogram of aid that is on these ships is a failure because all these people on these ships giving up their time to help their fellow human beings are doing what their governments are legally obliged to do."
The World Health Organization has said that even during armed conflicts, states are obligated under international humanitarian law to ensure that people are able to reach medical care in safety.
"This is a mission that aims to open a humanitarian corridor so the aid delivery organisations can arrive," Saif Abukeshek, a Palestinian activist and member of the flotilla's organising committee, said.
Activists on last year's flotilla said they were subjected to inhumane conditions during their detention by Israeli forces - an allegation that was rejected by an Israeli foreign ministry spokesperson.
