WASHINGTON (AP) -- U.S. officials alerted states Thursday to immediately inspect all bridges similar to the Minneapolis bridge that collapsed into the Mississippi River, killing at least four people.

Transportation Secretary Mary Peters signed off on an advisory that was sent by the Federal Highway Administration urging state transportation departments to conduct inspections of bridges similar to the steel-deck truss bridge that collapsed Wednesday.

There are approximately 700 such spans, according to department spokesman Brian Turmail. He did not have a list of bridge locations.

"We don't know what caused this span to collapse, but the secretary wants to make sure that states are taking every possible precaution," said Turmail.

The bridge that collapsed during rush hour Wednesday evening was built in 1967, rose 64 feet (19.51 meters) above the river and stretched 1,900 feet across the water. It was built with a single 458-foot-long (140-meter) steel arch to avoid the need for piers that might interfere with river navigation.