The ship was part of a four-vessel Freedom Flotilla Coalition that left from Denmark in May with the aim of breaking the crushing 12-year Gaza blockade imposed by Israel and neighbouring Egypt.

Its last reported position before losing contact with the flotilla was 40 nautical miles from Gaza’s coastline, the group said in a statement on Saturday.

“We demand that the Israeli occupation forces not interfere with our unarmed yacht as we continue our voyage to Gaza to deliver our gift of much-needed medical supplies,” Dror Feiler, a spokesman for the coalition, said.

Two million people living in Gaza lack access electricity, food, healthcare and other basic services, according to the UN, with conditions in the enclave set to become “unliveable” by 2020.

Repeated interceptions

The Israeli army said in a statement the vessel was monitored and intercepted in accordance with international law. Those on board were held for “further inquiry”.

It was the second flotilla vessel held by Israeli authorities in a week, after naval forces seized a Norwegian-flagged boat carrying at least 23 people on Sunday.

The interceptions follow a number of failed attempts by activists to reach Gaza’s coastline in recent years.

In 2015, a flotilla of four boats bound for Gaza was forcibly redirected to Ashdod.

In 2010, an attempt to reach the enclave by the Turkish Mavi Marmara flotilla proved fatal when Israeli commandos stormed the ship, killing nine Turkish nationals.

¡La libertad encarcelada!, los 12 activistas, tripulación y periodistas del velero # Freedom de @ GazaFFlotilla tras ser asaltados en aguas internacionales y secuestrados son encarcelados por Israel por intentar romper el # bloqueo de # Gaza y llevar suministros médicos a hospitales.

In May, a flotilla carrying at least 25 patients, students and activists broke Israel’s imposed boundary off the coast of the Gaza Strip for the first time in more than a decade.

Israel prohibits ships from travelling more than six nautical miles from Gaza’s coastline.

The vessel, however, travelled nine nautical miles offshore before four Israeli warships flanked it and diverted it to Ashdod.