The United Arab Emirates has told UN members that a state was likely to be behind “sophisticated and coordinated” attacks on four tankers off its coast last month.

The attacks required expert navigation of fast boats and trained divers who likely placed limpet mines on the vessels under the waterline to incapacitate but not sink them, according to the preliminary findings of a joint investigation by the UAE, Norway and Saudi Arabia, The Guardian reports.

In a briefing document given to UN security council members, the three countries did not say who they believed was behind the attacks. Iran has been accused by the US of being responsible.

“While investigations are still ongoing, these facts are strong indications that the four attacks were part of a sophisticated and coordinated operation carried out by an actor with significant operational capacity, most likely a state actor,” the document said.

The countries believe the attacks were the work of several teams of operatives who coordinated the timed detonation of all four explosive charges within an hour.