U.S. intelligence officials have received threats that terrorists will strike a U.S. nuclear power plant July 4, and are reviewing the information to determine whether it is reliable.

The government is taking the threats seriously, though officials have preliminarily determined that the information is not credible enough to act upon, said officials familiar with the investigation.

The officials, who spoke on condition of anonymity, said the alleged plot to attack on America's celebration of independence is one of scores of threats filtering through U.S. intelligence and is not considered serious enough to formally warn the public or change the nuclear industry's already high level of alert.

The threat received last week suggested that an unidentified Islamic terrorist group was planning to attack a nuclear power facility in the Northeast, officials said. It did not specify a target.

Unlike some other recent threat information, the power plant threat did not come from Abu Zubaydah, the senior Al Qaeda operational leader in U.S. custody. Abu Zubaydah's interviews with U.S. interrogators led a recent warning to banks, and heightened concerns Al Qaeda was developing a radiation-spreading dirty bomb.

Rep. Edward Markey of Massachusetts, a senior Democrat on the House Energy Committee, said that while he didn't know if the threat was credible, it indicated that "Al Qaeda is seriously targeting U.S. nuclear facilities for future attacks."

He said he is urging the Nuclear Regulatory Commission to take such steps as restoring a no-fly zone within a 10-mile radius of nuclear plants, federalizing the security force and conducting more extensive background checks of all plant employees.

The Washington Times first reported the threat.