Al-Qaeda's wing in Yemen claimed responsibility for Sept. 15 attacks on oil facilities in the Arab state and vowed more strikes against the US and its allies.
"Let the Americans and their allies among the worshippers of the cross and their apostate aides ... know that these operations are only the first spark and that what is coming is more severe and bitter," the group said in a statement posted on the Internet.
The authenticity of the statement posted on a Web site used by Islamist militant groups could not be verified. The statement, believed to be the first posting by Yemen's branch of al-Qaeda, was dated Ramadan 20, which corresponds to Oct. 13.
A US intelligence official, speaking on condition of anonymity, said analysts were working to try to verify the authenticity of the posting.
"We know there is now some sort of organization that calls itself al-Qaeda Yemen," the US official said. "We think they've been trying to get this up on a Web site for a while."
Yemen had said that four bombers were killed on Sept. 15, when security forces blew up four rigged cars before they reached oil and gas facilities in the eastern provinces of Marib and Hadarmout. A worker with Canadian oil company Nexen Inc was also killed.
The attempts came days after al-Qaida's No. 2, Ayman al-Zawahri, issued a videotaped threat of attacks on the Persian Gulf and on facilities he blamed for stealing Muslim oil.
Commenting on the foiled attacks, the group said: "These operations came in response to directives from our emir [leader] Sheikh Osama bin Laden, may God preserve him, in which he ordered Muslims to hit the Western economy and stop the robbing of Muslims' wealth."
The group also said Yemeni President Ali Abdullah Saleh should "repent, return to his faith, apply Islamic law, renounce democracy, the religion of America and abandon [his] alliance with the infidels."
"Let him [Saleh] know that his rule will not last [forever] and that God bestows his victory upon his soldiers ..."
Saleh, who has ruled Yemen since 1990, has cracked down on al-Qaeda after the Sept. 11, 2001, attacks on the US and bombings in the Arab state.
"Let them know that our blood is not cheap. The killing of Sheikh Abu Musab al-Zarqawi will not pass without revenge ... let the tyrant of Yemen know that the killing of Sheikh Ali al-Harthi by US missiles will not pass without revenge," the statement continued.
Harthi, al-Qaeda leader in Yemen, was killed by a missile fired by an unmanned CIA plane in Yemen in 2002 and Iraq's al-Qaeda branch chief Zarqawi was killed in a US air strike in June. It said the operations were named after the two men.
Yemeni officials were not immediately available for comment, but the US intelligence official said the group appears to be trying to emerge as an organization.
"They clearly have tried to be organized. They carried out attacks in September that showed some semblance of an organization. But whether this is from them or bears that mark, I don't know," he said.