The government Wednesday pressed ahead with the trial of a Palestinian whose detention may have provoked a cruise ship massacre and said it would not allow Greece to become an arena for terrorist battles. A previously unknown group linked with Palestinians claimed responsibility for Monday's attack on the City of Poros cruise ship. The Organization of the Martyrs of the Popular Revolution in Palestine, took responsibility in a statement delivered Wednesday to a Western news agency in west Beirut. Radio France-Inter in Paris, meanwhile, reported that an anonymous caller said in a rambling conversation that the pro-Iranian group Islamic Jihad carried out the attack to avenge the U.S. downing of an Iranian passenger plane. There was no way to authenticate either claim. The PLO has condemned the attack on the City of Poros. Tourists were sunbathing and strolling on the ship's deck Monday when several terrorists pulled machine guns and began shooting and throwing hand grenades. Nine people were killed, and 98 were wounded. Merchant Marine Minister Evangelos Yiannopoulos told Parliament Wednesday that the terrorists returned to shore in rescue boats and had not escaped in a waiting speedboat as police initially reported. Many vessels rushed to the ship's aid and rescued panicked passengers who had jumped overboard to escape the attack. An Athens radio station reported that one of the terrorists was a woman who received treatment in the hospital for a foot injury after the attack. The station identified her as Aysal Lampsalmi, a Moroccan passport-holder, and said she checked out of the Tzanneion Hospital in Piraeus on Monday night with other survivors who sustained slight injuries. Greek authorities believe the guerrillas who carried out the attack may have intended to hijack the ship to win freedom for Mohammed Rashid, a Palestinian. Rashid is wanted by the U.S. government for allegedly planting a bomb on a Pan Am jet in 1982 that killed one person and injured 15. He is charged in Greece with entering the country on a forged passport. His trial had been delayed until the end of July, but Justice Minister Agamemnon Koutsogiorgas overruled that decision Wednesday and ordered proceedings to begin. Rashid told reporters at the courthouse that he was not a terrorist and claimed the ship attack was ``an American operation ... to distract attention from the shooting down of the Iranian plane and the Palestinian uprising'' against Israel's occupation of the West Bank and Gaza Strip. ``The Americans can say what they like ... I had nothing to do with anything,'' he said. Rashid's trial was held over until Thursday because his lawyer and interpreter were unavailable. The deputy minister for tourism, Nikos Skoulas, said Greece was determined not to become ``an arena for different groups or factions to settle their differences.'' ``We are not soft or weak on anyone. That accusation has been leveled at us,'' he added, referring to past criticism by the United States for laxity in combating terrorism. Skoulas said security officers were being posted on the one-day Greek island cruises operated by the City of Poros and other vessels. Confusing and sometimes contradictory information obscured many details about the attack. The statement signed by The Organization of the Martyrs of the Popular Revolution in Palestine said the attack was ``in retaliation for the escalation in the operations of murder and extermination by the murderous Zionist-American gangs in Palestine, Lebanon, the gulf and all over the world.'' It also claimed responsibility for a car bomb that killed two men near the liner's home dock of Piraeus about six hours before the ship attack. Police speculated that automatic weapons, grenades and explosives found in the car were intended for hijacking the ship. In Baghdad, Iraq, Bassam Abu Sharif, spokesman for PLO chief Yasser Arafat, declared, ``The Palestine Liberation Organization and the Palestinian people, being themselves victims of state-organized terrorism, strongly condemn this criminal attack on the Greek ship and the car bombing.'' Security police backtracked on an earlier claim that a young woman with a French passport was among the terrorists. But they said a woman was still believed to be among the terrorists. It remained unclear how many terrorists were involved. Most accounts by survivors and authorities varied between three and four. The death toll has also varied. The harbor authority initially said 11 people died, and the coroner said there were 10 bodies. On Wednesday, the government finally said the official death count was nine. It said confusion apparently arose because bodies were badly charred and some were dismembered.