The manhunt was launched following "credible and specific" information that the trio would be carrying out terrorist attacks with explosive laden vehicles in cities like New York and Washington, which has forces authorities to elevate the threat level nationwide.
Multiple media reports said the threat involved a car-or truck-bomb attack aimed at bridges or tunnels in New York or Washington.
NBC reported that US law-enforcement officials have been alerted to watch for three men "of Middle Eastern descent," possibly riding in a van.
Several top government officials and lawmakers having access to classified intelligence information said that the information about the terror plot has been received from a credible one source, which has proved valuable in the past, but could not be corroborated yet.
"This is somebody who in the past has been a source of reliable information. But the people being quoted are not that person. The information is specific enough that it deserves to be taken seriously. And I'm very grateful that we are," Senator Joseph Lieberman told the CNN.
"Well that's about as specific and general as the evidence or the intelligence is, those two cities (New York and Washington), and I would say that people should be alert. I don't think anybody should be panicked," he said.
"When an administration comes to a decision about whether to let this information out that there is something that we picked up that suggests that there might be an attack being planned, they've always got to make a judgment about whether to make it public. Making it public sometimes jeopardise sources. But in this case, I think it's important because it alerts everybody to be on guard this weekend and be careful," Lieberman said.
A US official said the source indicated Al Qaeda's new leader Ayman al-Zawahri was involved in planning the plot. But the official also said that many in the intelligence community question that and other aspects of the source's information, Politico reported.
US Secretary of State Hillary Clinton said there is a specific, credible, but unconfirmed threat report. "We take it seriously, as we always do, and particularly because we learned from the raid on bin Laden's headquarters and going through all of the material that Al Qaeda was still determined to attack around anniversaries and particularly New York and Washington," she said.
"It is a real threat," Vice President Joe Biden told the CBS news.
White House Press Secretary Jay Carney told a group of foreign journalists that US President Barack Obama instructed the homeland security team to redouble their efforts to ensure that every precaution is being taken, to every avenues being explored to pursue the information that they have about those threats and develop those information.
Carney said some four months ago Obama had ordered his top counter-terrorism official, John Brennan, to run to ground, as they say, every potential lead.
"And as late as Tuesday the president chaired a meeting with his homeland security team, to review those progress, to review those situation so," he said.
