VIENNA, Austria – A Bosnian who tried to enter the U.S. Embassy in Vienna with a backpack filled with explosives, nails and Islamic literature was arrested yesterday after the bag set off a metal detector and the man fled on foot, authorities said.

Police sealed off the neighborhood as a precaution and shut down or rerouted nearby bus and tram lines. Officers patrolled the area with bomb-sniffing dogs.

The suspect was described only as a 42-year-old native of Bosnia-Herzegovina who now lives in the province of Lower Austria, which encircles most of the capital. Police said they made the arrest a short distance from the embassy in a neighborhood where security is tight.

The motive for the attack was not immediately clear. Vienna police spokeswoman Michaela Raz said explosives experts were examining the contents of the backpack, which contained at least two hand grenades.

“There were a lot of nails in that bag. Had it exploded, it would have had an enormous shrapnel effect,” said Doris Edelbacher, of Austria’s federal counterterrorism office.

Munitions experts were still trying to determine whether the device had been properly rigged to explode.

The suspect spoke broken German and appeared to ramble during an initial interrogation, Edelbacher said.

It was unclear how far he made it into the embassy. Public broadcaster ORF, citing unidentified officials, reported that a metal detector sounded an alarm as the man was passing through security checks and that he fled immediately.

The nature of the Islamic material he allegedly was carrying also was unclear.

Embassy officials could not immediately be reached for comment.