Washington Remains Secure Despite Crowds

Authorities monitored a rush of intelligence leads Tuesday at the largest security operation in presidential inauguration history, including a possible threat from an East Africa radical Islamic terrorist group.

Law enforcement and intelligence officials received information that people associated with a Somalia-based group, al-Shabaab, might try to travel to the U.S. with plans to disrupt the inauguration, according to a joint FBI/Homeland Security bulletin issued Monday night. The information had limited specificity and uncertain credibility, said Homeland Security spokesman Russ Knocke.

U.S. counter-terror officials have grown concerned in recent months about the threat posed by the militant al-Shabaab group and a cell of U.S.-based Somali sympathizers who have traveled to their homeland to "fight alongside Islamic insurgents," the alert reported.

"Authorities stress this potential threat is not corroborated, and only of limited specificity," reports CBS News correspondent Bob Orr. "The bulletin is being circulated out of an abundance of caution.

"There is no change in the overall security posture, and no change in the nation's threat level," adds Orr.

Officials have warned that the inauguration poses an attractive target for terrorists because of the large crowds descending on the nation's capital and the historic significance of the country swearing in its first black president.

"As always, we remind the public to be both thoughtful and vigilant about their surroundings, and to notify authorities of any suspicious activity," Knocke said.

A senior law enforcement official familiar with the security operations said the Somali alert had been posted to make sure no effort was spared. The official spoke on condition of anonymity because he was not authorized to speak publicly about security matters. The official said authorities have been monitoring suspicious chatter referring to the inauguration in recent days, but as of late Monday night, they felt comfortable with security preparations.

There was an unprecedented amount of security Tuesday, with thousands of law enforcement officers from 58 federal, state and local agencies working together. Sirens keening, squad cars and utility vehicles swept along downtown streets even before dawn, racing to cordoned checkpoints as crowds gathered.

Knocke said officials consistently monitor all threat information, as they always do.

There has been no change in the terrorist threat level, which remains at yellow - or elevated.

Just before 9 a.m. the U.S. Park Police closed the Mall between 4th and 14th streets and were directing people to the grounds of the Washington Monument due to the crowd size, Park Police spokesman Robert Lachance said.

"We watched the crowd push against a line of about 10 National Guardsmen," reports CBS News correspondent Kimberly Dozier. "It was good-natured, but got a little heated, and the guardsmen finally said, 'We can't hold this,' and gave up.

"Now people are thronging through the gates, crawling over the jersey barriers, taking apart the metal gates and walking through."

Washington police say there have been just a few scattered incidents of people in medical distress, but paramedics have not had a difficult time reaching people. As of late morning, there was no widespread health issue relating to the size of the crowd and the cold.

D.C. fire and EMS department spokesman Alan Etter said everyone who has needed help has eventually received treatment.

"Obviously the crush of people downtown is making it very challenging," Etter said. "We're doing the best we can."

Between 4 a.m. until 10 a.m., the fire department responded to more than 60 calls from people falling down or complaining of the being cold, Etter said. About 20 people have been hospitalized.

In addition, one person was struck by a subway train, prompting Metro officials to close two stations and turn around some trains. Metro has been running at crush capacity since 4 a.m.