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The Bush administration said Wednesday that the United States and its allies have begun a campaign to disrupt terrorist operations on the basis of the intelligence that led to the elevation of the terror threat level over the weekend.

In Britain, authorities said they were questioning 12 men detained on suspicion of having ties to terrorists.

American officials said at least some of the arrests in Britain on Tuesday were linked to the discovery in Pakistan of intelligence information that included evidence of reconnaissance of targets in the United States by Al Qaeda.

One senior American official said the United States was especially interested in one of the men detained in Britain, Abu Moussa Al Hindi, who is believed to be a high-level Al Qaeda operative.

White House press secretary Scott McClellan said Wednesday that “there are some ongoing operations under way” to disrupt terrorist activity. Officials earlier said the Sunday alert was driven in part by intelligence beyond information about specific buildings in Washington and the New York City area.

It was not clear whether the arrests in Britain were directly linked to the apparent risk of an attack on the buildings. One senior official in Washington said there were “possibly” direct ties.

The official described the arrests as “part of this web that emanates from Pakistan.”

The official said that “what you saw in the U.K. was a result in part of information gained” from the arrest last month of Mohammad Naeem Noor Khan, the Pakistani computer engineer whose capture led the CIA to computer files detailing the reconnaissance of financial institutions.

As information came into the White House over the weekend, National Security Adviser Condoleezza Rice called her counterparts in countries including Pakistan, Saudi Arabia and Jordan to request help from their intelligence services, a government official said.

Other officials signaled that there were intensified efforts under way by the FBI to determine whether there were Al Qaeda operatives inside the United States.

The reports allegedly found on Khan’s computer hard drive about the buildings in the United States were written in what one White House official has described as “perfect English,” suggesting that the surveillance may have been carried out by, or with the help of, an American or someone who had spent considerable time in an English-speaking country. Kahn speaks English and studied in London.