A shadowy Islamist group which claimed it carried out last week's suicide bombing in Qatar said in an Internet statement it was responsible for an oil refinery explosion in Texas that left 15 people dead. "It was a new kind of operation as we promised before," said the "Jund al-Sham Organization" (Organization of Soldiers of the Levant) in the statement posted on an Islamist Web site and dated March 24. "Jund al-Sham is able to attack with an iron fist all the enemies of Allah wherever they are," added the statement, whose authenticity could not be verified. "This operation was a big surprise, which we spoke of in other statements, and we will continue our suicide operations inside and outside America, and we will attack the economy of America as America did the economies of the Muslims," it added. The group also threatened to carry out attacks in Britain and Italy, and said these would continue "until the last soldier of the Crusaders or Jews is no longer in an Islamic country."The U.S. Federal Bureau of Investigation has rejected claims purportedly from two Islamist groups of responsibility for Wednesday's blast, which rocked the third-biggest petrochemical complex in the United States, run by British multinational BP at Texas City. "We've found no evidence to support criminal or terrorist activity," Al Tribble, spokesman for the FBI office in Houston said Thursday. He said he did not know the names of the groups, which made the claims through e-mails. BP said the cause of the blast was still being investigated, but has ruled out terrorism.