WASHINGTON -- U.S. intelligence analysts reviewing secret data and electronic intercepts have found no credible evidence of plans to disrupt the inauguration of President-elect Barack Obama, Department of Homeland Security Secretary Michael Chertoff said.

"Everybody has been very focused on this for months," he said in an interview Thursday.

Michael Chertoff

Mr. Chertoff said he is as "confident as humanly possible" that there is no evidence of a terrorist threat but still believes the event would be an attractive target, especially for "lone offenders."

That is the thrust of a joint threat assessment completed this week by his department along with other U.S. intelligence and law-enforcement agencies.

The assessment, dated Wednesday and reviewed by The Wall Street Journal, concluded there was no specific evidence of a credible threat, but said the Jan. 20 inauguration would be a high-value terrorist target because of its historical significance and expected crowds of between 1.5 million and 2 million people.

The Secret Service, which is part of the Department of Homeland Security, is responsible for coordinating security, along with about 13,000 personnel from 94 law-enforcement agencies and the military. The inauguration has been declared a "national security special event," giving the agency special powers.

Mr. Chertoff said even a single individual could pose a serious danger to crowds, given the expected sea of revelers and the government's limited ability to screen those farthest from the day's main events. Security will increase in areas closest to Mr. Obama and other VIPs, including the inaugural-parade route.

"The thing you most worry about is a single individual on his own building a bomb, a small bomb, or picking up a gun," Mr. Chertoff said. "The closer you get to where the events are, the harder it will be to smuggle that in."

Officials looking at possible lone-offender threats haven't found anything that has "progressed past rhetoric to operational planning," according to the assessment.

The intelligence review reported a high level of rhetoric aimed at Mr. Obama: "The President-elect has been the focus of voluminous threat-related reporting since announcing his candidacy, and the number of threat reports has increased since his election."

It also said the inauguration of the first minority president in the U.S. "increases the potential threat, particularly stemming from individuals on the extremist fringe of the white supremacist movement."

It also notes, however, that no organized group "is known to have expressed a direct threat to the President-elect or the inauguration."

Write to Cam Simpson at cam.simpson@wsj.com