Investigators from three countries have boarded the damaged French supertanker Limburg in the Gulf of Aden in an effort to determine the cause of a deadly explosion on Sunday. Meanwhile, a militant Yemeni group is reported to have claimed responsibility for the blast, and a Yemeni official has acknowledged for the first time that this might have been a terrorist act.

U.S, French and Yemeni anti-terror experts boarded the crippled Limburg Thursday. The investigators are trying to determine if Sunday's blast, which killed one of the ship's 25 crewmembers, was an accident or a terrorist attack.

For the first time since Sunday's explosion, a senior Yemeni official has said the explosion might have been deliberate. The Minister of Transportation and Maritime Affairs, Said Yafai, told reporters Thursday that Yemen is not ruling out any possibility, but he said the government also does not want to jump to any conclusions about the blast while the investigation continues.

Yemeni officials have repeatedly insisted the explosion was an accident. But one official has said regardless of the outcome of the investigation the government will not try to conceal the truth.

Meanwhile, an Arabic newspaper reports it received a statement from a militant Islamic group in Yemen claiming responsibility for the explosion. The London-based newspaper Asharq al-Awsat says the Aden-Abyan Islamic Army sent a statement claiming it carried out the attack against the Limburg to avenge the execution of one of its leaders, who was convicted of helping to kidnap 16 foreign tourists in 1998. The Aden-Abyan group is accused of committing several such kidnappings and also several bombings. And one of its members is being held for questioning in Sunday's blast.

The Limburg explosion happened in waters off the coast of a part of Yemen where militant groups are particularly strong.