Because of the timing

LONDON - NBC News has learned that U.S. and British authorities had a significant disagreement over when to move in on the suspects in the alleged plot to bring down trans-Atlantic airliners bound for the United States.

A senior British official knowledgeable about the case said British police were planning to continue to run surveillance for at least another week to try to obtain more evidence, while American officials pressured them to arrest the suspects sooner. The official spoke on condition of anonymity due to the sensitivity of the case.

In contrast to previous reports, the official suggested an attack was not imminent, saying the suspects had not yet purchased any airline tickets. In fact, some did not even have passports.

The source did say, however, that police believe one U.K.-based suspect was ready to conduct a dry run. British authorities had wanted to let him go forward with part of the plan, but the Americans balked.

At the White House, a top aide to President Bush denied the account.

There was unprecedented cooperation and coordination between the U.S., the U.K. and Pakistani officials throughout the case, said Frances Townsend, Assistant to the President for Homeland Security and Counterterrorism, and we worked together to protect our citizens from harm while ensuring that we gathered as much info as possible to bring the plotters to justice. There was no disagreement between U.S. and U.K. officials.

Another U.S. official, however, acknowledges there was disagreement over timing. Analysts say that in recent years, American security officials have become edgier than the British in such cases because of missed opportunities leading up to 9/11.

Aside from the timing issue, there was excellent cooperation between the British and the Americans, officials told NBC.

The British official said the Americans also argued over the timing of the arrest of suspected ringleader Rashid Rauf in Pakistan, warning that if he was not taken into custody immediately, the U.S. would render him or pressure the Pakistani government to arrest him.

British security was concerned that Rauf be taken into custody in circumstances where there was due process, according to the official, so that he could be tried in British courts. Ultimately, this official says, Rauf was arrested over the objections of the British.

The official shed light on other aspects of the case, saying that while the investigation into the bombing plot began months ago, some suspects were known to the security services even before the London subway bombings last year.

He acknowledged that authorities had conducted electronic and e-mail surveillance as well as physical surveillance of the suspects.

Monitoring of Rauf, in particular, apparently played a critical role, revealing that the plotters had tested the explosive liquid mixture they planned to use at a location outside Britain. NBC News has previously reported that the explosive mixture was tested in Pakistan. The source said the suspects in Britain had obtained at least some of the materials for the explosive but had not yet actually prepared or mixed it.