Israel's foreign ministry has branded it a "selfie yacht", while Thunberg says she has been "kidnapped" after Israeli forces boarded the vessel.

Israeli forces seized a Gaza-bound aid boat and detained Greta Thunberg and other activists who were on board early Monday, enforcing a longstanding blockade of the Palestinian territory that has been tightened during the war with Hamas.

Israel has intercepted a Gaza-bound aid ship carrying Greta Thunberg and other prominent activists, detaining those onboard, with the vessel being taken to Israel.