The vessel was headed towards the Bab al-Mandeb strait at the entrance to the Red Sea when six pirates aboard four vessels attempted to board it, drawing warning shots from the Iranian navy, ISNA said.

It is the second such incident involving Iranian shipping in recent weeks after pirates attacked a convoy of two vessels on October 16.

Like other countries dependent on the shipping route through the Red Sea and Suez Canal, Iran stepped up its naval presence in the Gulf of Aden after a wave of attacks by Somalia-based pirates between 2000 and 2011.

But the number of attacks has fallen sharply in recent years.