The United Nations called Wednesday for an investigation into alleged drone attacks against a Gaza-bound aid flotilla that prompted Italy and Spain to send naval ships to help.

The Global Sumud Flotilla, carrying activists including Swedish environmentalist Greta Thunberg, blamed Israel for more than a dozen explosions heard around its vessels off Greece late on Tuesday.

U.N. Human Rights Office spokesperson Thameen Al-Kheetan said anyone responsible for the "violations" should be held accountable, and called for an "independent, impartial and thorough investigation."