Amtrak police stopped and searched three trains, including two Acela Express (search) high-speed trains traveling from New York to Washington, a spokesman for the passenger railroad said.

One Acela train was north of Philadelphia when it was stopped Thursday night. The other was near Baltimore-Washington International Airport (search). Details about the third train were not immediately available.

"As a precaution we stopped three trains, and nothing was found at all," said Amtrak spokesman Dan Stessel. "They were searched last night based on an anonymous noncredible threat called into the Baltimore City Police Department."

Amtrak police officers and dogs searched the trains. Delays ranged from 20 to 60 minutes, Stessel said.