Swedish climate activist Greta Thunberg and other passengers aboard a fleet of Gaza-bound aid ships have been detained by the Israeli military after more than a dozen vessels of the Global Sumud Flotilla were intercepted, sparking global outcry.

The flotilla is trying to break Israel’s 18-year blockade of Gaza and get aid into the war-ravaged enclave using ships that set sail from ports across the Mediterranean. As of around 7 a.m. local time Thursday, 29 GSF boats were still sailing and were about 46 nautical miles from Gaza, while 15 boats had been intercepted, according to GSF’s tracker.

Flotilla organizers labeled Israel’s interception of the ships “an illegal attack” on humanitarians, while Israel said the activists were “not interested in aid, but in provocation.