By John O'Callaghan

WASHINGTON, July 2 (Reuters) - Homeland Security Secretary Michael Chertoff on Monday played down a report that al Qaeda was planning a spectacular attack on the United States, saying there was no credible information about an imminent threat.

As British police investigated two failed car bombs in London and a fiery attack on Glasgow's airport by a fuel-filled vehicle, U.S. officials tightened security at transport hubs without raising the country's overall alert level.

"We do not currently have any specific threat information that is credible about a particular attack on the United States," Chertoff told Fox News.

ABC News, quoting a senior U.S. official, said on Sunday a secret law enforcement report prepared for the Department of Homeland Security warned that al Qaeda planned to carry out a spectacular attack this summer.

"This is reminiscent of the warnings and intelligence we were getting in the summer of 2001," ABC quoted the unidentified official as saying.

The United States has been on heightened alert since the Sept. 11, 2001, attacks by al Qaeda using hijacked airliners. Britain is also a target for Islamic militants for its role as Washington's ally in the wars in Iraq and Afghanistan.

FURTHER ATTACKS

"Al Qaeda and its affiliates do intend to carry out further attacks against the United States and the West," Chertoff said.

"We also know that they tend to want to do attacks that are spectacular or high-profile, so it's not surprising to have analysts comment on the fact that this kind of an attack is a very definite possibility," he said.

"But again I want to say that's more general analysis that is not based on a specific piece of information about a particular attack."

Chertoff had made similar comments in interviews on Sunday about the possibility of a specific security threat to the United States.

British authorities have linked the three incidents late last week to al Qaeda and detained seven people as part of an investigation that police say is likely to yield more arrests.

"I wouldn't rule al Qaeda out," Chertoff said.

"We have seen, however, different kinds of attacks. Sometimes there are al Qaeda-affiliated groups that use different methods than what we might call core al Qaeda."

The great lesson from the British plots, he said, was the two London attacks were foiled partly because people saw something suspicious and alerted the authorities.

"We are in very close contact with British authorities and have been since this whole episode began a few days ago," Chertoff said.

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