BALTIMORE -- Authorities closed one of two highway tunnels carrying traffic under Baltimore's harbor for nearly two hours Tuesday and partially shut the other because of a threat to detonate vehicles full of explosives inside the tubes.
The Baltimore Harbor Tunnel was closed and the Fort McHenry Tunnel was reduced to one lane of traffic in each direction, said Lt. Col. David Franklin of the Maryland Transportation Authority Police. The closures began about 11:30 a.m. and officers began reopening the tubes about 1:15 p.m.
"The safe thing right now is to allow these tunnels to reopen," said chief Gary McLhinney of the transportation authority police.
He said the investigation was continuing, led by the FBI.
The tunnels carry Interstates 95 and 895 between Washington and the Philadelphia and New York city areas.
A federal law enforcement official, speaking on condition of anonymity, said the threat was phoned in to authorities by a person claiming to have information from abroad.
Even though authorities questioned the credibility of the threat, they were looking for several men in the Baltimore area who the source said would drive "explosives-laden vehicles" into the tunnel, said another federal law enforcement official, who also spoke on condition of anonymity.
The decision to close the tunnel was made by state and local, not federal, authorities, that official said.
"We're acting out of an abundance of caution," said Jim Pettit, a spokesman for Gov. Robert Ehrlich's homeland security office.
"While the information was somewhat specific, to date the intelligence community has not found evidence that corroborates the information. This is an ongoing investigation," FBI special agent Richard Kolko said.
McLhinney said vehicles were stopped but he would not say what police were looking for. He did say nothing had been found as of early afternoon.
Interstate 95, which uses the Fort McHenry Tunnel, is a key north-south artery through East Coast states, stretching from Maine to Florida, serving cities including New York, Philadelphia and Washington. Interstate 895, which uses the Harbor Tunnel, is an alternate north-south link through Baltimore.
On Oct. 6, a threat prompted authorities in New York to sharply increase security in the city's subway system. Several days later, local officials announced there was no clear evidence an attack would be carried out and scaled back the protection.
Associated Press writer Mark Sherman in Washington contributed to this story.