Avigdor Lieberman, Israel's hardline foreign minister, warned that the development posed a new threat to the country's security. He said: "To my regret, the international community is not showing readiness to deal with the recurring Iranian provocations. The international community must understand that Israel cannot forever ignore [them]."

The Iranian move appeared designed to test the stance of the new Egyptian regime to Tehran following the departure of President Hosni Mubarak, who was an implacable foe of the Islamic Republic.

A spokesman at the Suez Canal Authority said no Iranian naval vessels had passed through the port since the 1979 revolution. "The Suez Canal does not deny any commercial ships from passing as long as we are not in a state of war," Ahmed El Manakhly, a member of the Suez Canal board, said. "For warships to pass through the canal, approval from the ministry of defence and the ministry of foreign affairs is needed and this applies to all warships owned by any country."

Washington said it was aware of the ships but had no information about what they were doing.

The destination of the ships was reported as Syria, which has been officially at war with Israel since 1967 and is Iran's main conduit for weapons supplies to Hizbollah, Israel's Lebanese enemy.

Mr Mubarak, the ousted president and his deputy Omar Suleiman policed Israel's southern flank, stopping arms shipments and weapons smuggling across the Sinai desert.

Israeli officials are now concerned that whatever new government emerges in Egypt will be hostile to its security. "We have had a very cold peace with Israel for thirty years that depended on Omar Suleiman on the Egyptian side to sort out problems," said a former senior Israeli official. "What happens now if the Egyptian military can't or won't act to prevent shipments. It is a very destabilising prospect."

Iran's four British-built Alvand frigates have sporadically patrolled the Gulf of Aden since 2007 on counter piracy missions.

Meanwhile regional protests continued to spread yesterday as hundreds took to the streets of Benghazi, Libya's second city, to call for the overthrow of Colonel Muammar Gaddafi. Protests also continued in Yemen, Bahrain and Iran.