Three cargo ships hijacked off the coast of Somalia

The attacks followed the seizure of a Malaysian palm-oil tanker with 39 crew in the same area late on Tuesday. It raised to seven the number of ships hijacked in the Gulf of Aden since July 20.

International Maritime Bureau piracy reporting centre chief Noel Choong said that three hijackings in one day "is unheard of."

In the first incident, pirates fired on the Iranian bulk carrier before boarding and commandeering it. Less than an hour later, the Japanese-operated tanker with 19 crew was attacked and seized nearby. The third ship was comandeered shortly afterwards.

Mr Choong urged the UN and the "international community" to "take serious action to stop this menace."

The bureau also issued an urgent warning to all ships in the Gulf of Aden to maintain a strict watch.