In a provocative move the ­Iranian Red Crescent was this weekend due to send two vessels packed with food and medical aid and 70 relief workers.

A third ship, carrying an operating theatre, could follow.

President Ahmadinejad raised the spectre of a sea battle as he warned the ships would be carrying an escort of “volunteer marines” ready to “teach Israelis a lesson”.

Ali Shirazi, the Revolutionary Guard’s spokesman for Supreme Leader Ayatollah Ali Khamenei, said it was “Iran’s duty to defend the innocent people of Gaza”. Foreign Secretary William Hague described the intervention as “unhelpful”.

The blockade has been in place since Hamas took control of Gaza in 2006 despite inter­national concern about a humanitarian crisis.

That concern turned to condemnation on May 31 when, in a raid on a Turkish aid flotilla, nine people were killed by Israeli commandos.