Shias called for death of Jews - then Sunnis blew them up

"Yemen is a failed state which is now part and parcel of the Sunni-Shia conflict," said Uzi Rabi, an expert on Yemen and the director of the Moshe Dayan Centre for Middle Eastern Studies at Tel Aviv University. "In the short term we will see a lot of trouble," he said, adding that "Yemen could be a winning formula for Palestinians looking to adopt strategies and tools from radical groups".

Yemen has been a focus of US counter-terrorism operations, but since its government, led by Ali Abdullah Saleh, was toppled by Houthi rebels in 2011, the country has descended into sectarian conflict.

The US has closed its embassy and pulled out its special forces owing to security concerns.

The Pentagon has said that it cannot account for the weaponry - worth $500m - that it has donated to Yemen to help the country fight its armed Islamist groups, according to a report published last week by the Washington Post.

US officials fear that money and supplies have been appropriated by the Houthi rebels - presumed to be backed by Iran - or by al-Qaeda.