(Adds IMB quote, detail) By Stefano Ambrogi LONDON, May 21 (Reuters) - The U.S. Navy has warned merchant ships to keep clear of the Somali coast after a series of pirate attacks, including one last week in which militia fired on a vessel with rocket-propelled grenades and machine guns. The warning, issued through the U.S. Navy's Maritime Liaison Office (MARLO) in Bahrain on Sunday, urged all merchant ships to stay at least 200 nautical miles off the east coast of Somalia. "Although there are coalition forces operating in the area, they cannot be everywhere monitoring every ship that passes the coast of Somalia," MARLO said. It urged merchant shipping to inform coalition forces of any suspicious activity immediately. The United Nations on Sunday called for international action against a "plague of piracy" off Somalia, saying it was threatening to cut off vital aid supplies to one million people. The International Maritime Bureau (IMB) watchdog on Monday gave details of two incidents that took place last week around 200 nautical miles off the coast of Somalia, marking a serious escalation in the pattern of attacks because they threatened trade lanes. Cyrus Moday, a senior analyst with the IMB in London, said it was "open season" for militants off Somalia because even if the perpetrators were caught there were no courts in the country to mete out justice. "Attacks have sprung up again because we believe there is no government in place to control the militants ... when the Islamists were in power there were no attacks," Moday told Reuters. He said out of 10 attacks off the Somali coast this year, five had taken place in May and three in April, clearly showing an upward trend. The IMB said the cargo ship Ibn Younus was on its way from Durban in South Africa to Jebel Ali in the Gulf when it was fired on with grenade launchers last week. It said none of the crew were injured in the attack, but the accommodation section was hit and caught fire. The vessel later managed to shake off its attackers. In the other attack, gunmen captured two South Korean ships and took scores of sailors hostage. The crews, who included Koreans, Chinese, Vietnamese and Indians, are still being held. Moday said that as the militia grew more audacious crucial trade routes linking the southeast Asia, the Gulf of Aden and Suez could be threatened. "That could be dangerous for everybody because Suez is a major route for international trade," he said. Piracy has been rife off Somalia since it slid into chaos after warlords toppled military dictator Mohamed Siad Barre in 1991. Many pirates claim to be "coastguards" protecting their waters against illegal fishing and dumping of toxic waste. The attacks have been on the rise since Islamists, who controlled most of south Somalia in the second half of 2006, were ousted in January.
