A row has broken out over the failure of an Irish Naval Service ship to fly the union jack while taking part in the tall ships festival in Belfast last month.

According to international protocol, it is customary when a ship visits a foreign port for the vessel to fly the flag of its own country as well as the country it is visiting.

However, the LE Eithne did not fly the union jack when it docked in Belfast port sparking controversy in the unionist community.

DUP MP Jeffrey Donaldson, whose Lagan Valley constituency is just on the edge of Belfast, said:

"I received a number of complaints from constituents who attended the tall ships event and who told me they were disappointed the Irish navy didn't honour the protocol. One would have hoped that post the agreement and the new political dispensation, we would have had the maturity to allow that kind of thing to happen without people evading it," he said.

"I would have no doubt that if the Royal Navy was visiting Dublin or Dun Laoghaire, they would comply with that protocol."

The unionist politician said that on the back of these complaints, he was taking the matter up with the British government.

An Irish Naval Service spokesman told the Sunday Tribune: "It's not practice that any warship would fly the flag of the country that they are visiting and it's not custom or practice for the Irish Naval Service. It's not just the Irish Naval Service which doesn't fly the flag of the country, it's lots of other navies as well."

However, the US navy has confirmed that it flies its own flag as well as the flag of the country it is visiting when it docks in foreign ports.

A US embassy spokesman said: "It's international regulations that the host country flag would fly at the front of the ship and the American flag at the back of the ship."