The canal is a vital global trading route and major source of revenues for the Egyptian authorities

Two Iranian naval ships have passed through Egypt's Suez Canal into the Mediterranean Sea heading for Syria, a source at the canal authority told the Reuters news agency.

The ships entered the canal at 03:45 GMT on Tuesday and passed into the Mediterranean at 13:30GMT, the Suez Canal Authority source said.

"Their return is expected to be on March 3," the source said.

The two vessels, Alvand, a patrol frigate and Kharg, a supply ship, are the first naval vessels going through the canal since Iran's 1979 Islamic revolution, after which diplomatic ties between Egypt and Iran were strained.

Egypt's ruling military council, facing its first diplomatic challenge since taking power on February 11, approved the vessels' passage through the canal.

The Suez Canal cuts through Egypt and allows shipping to pass from the Middle East to Europe and vice versa without going around the southern tip of Africa. The canal is a vital global trading route and a major source of revenue for the Egyptian authorities.

Israel takes a "grave view" of the passage of the ships. 

On Sunday, after a weekly meeting of his cabinet, Binyamin Netanyahu, the Israeli prime minister, denounced the ships' arrival in the region as an Iranian  power play.

And last week, the prospect of the Suez crossing was described by Avigdor Lieberman, Israel's far-right foreign minister, as a "provocation" by Iran.

But an Iranian diplomat said that: "This will be a routine visit, within international law, in line with the co-operation between Iran and Syria, who have strategic ties.

"The ships will spend a few days in Syrian ports for training purposes, having already visited several countries including Oman and Saudi Arabia."

The decision was a difficult one for Egypt's interim government as Cairo is an ally of the US and has a peace treaty with Israel.

However, Egypt's official MENA news agency has reported that the request for the ships to transit the canal was granted because they were not carrying weapons or nuclear and chemical materials.

The 1,500-tonne Alvand is normally armed with torpedoes and anti-ship missiles, while the larger 33,000-tonne Kharg has a crew of 250 and facilities for up to three helicopters, Iran's official Fars news agency said.