Austrian authorities said Tuesday they arrested a second Bosnian suspect in an apparent plot to bomb the U.S. Embassy in Vienna, and that the would-be bomber had contacted the embassy before the attempt.

Officials said they were treating the latest suspect as a possible accomplice of Asim C., a 42-year-old unemployed Bosnian arrested Monday after he tried to enter the embassy with a backpack containing grenades, plastic explosives and bits of metal.

The public prosecutor's office said police took Mehmed D., 34, into custody Monday night in Tulln, a town about 15 miles west of Vienna.

Investigators said both men were citizens of Bosnia-Herzegovina who lived in Tulln and knew each other. The suspects' last names were not released, in line with Austrian privacy laws.

Asim C. was arrested Monday after his bag — packed with the explosives and several handfuls of nails and screws apparently intended to serve as shrapnel — set off a metal detector at the entrance to the heavily fortified embassy, which is guarded by U.S. Marines.

He fled on foot, but was captured a short distance away after tossing the backpack into the street. It did not explode, and no one was injured.

Erik Buxbaum, Austria's general manager for public security, told reporters Tuesday that Asim C. said Mehmed D. had told him to bring the backpack to the embassy, and gave investigators his name and an address. But Buxbaum said Mehmed D. vehemently denied any involvement.

Oolice searched both men's homes and found about half a kilogram (one pound) of explosives in Asim C.'s home, Buxbaum said.

Rudolf Gollia, Buxbaum's spokesman, later told The Associated Press that Asim C. had "telephone contact" with the embassy beforehand. He declined to say when it had taken place.

Buxbaum said it was unclear whether the explosives were properly rigged to go off because the grenades were not fitted with detonators.

Police said Asim C. was carrying a book containing references to Islam. The Kurier newspaper published what it said was a photo of the book, which appeared to be a Muslim prayer manual.

Muslims comprise the predominant ethnic group in Bosnia-Herzegovina, and though the vast majority are moderate or secular, authorities there have been monitoring individuals who have become radicalized and are believed to have ties to extremists.

But Doris Edelbacher, chief spokeswoman for Austria's federal counterterrorism office, played down speculation Tuesday that the thwarted attack may have been motivated by radical Islamic ideology.

"It is too early to speak of an Islamist background," Buxbaum said.

Edelbacher said Asim C. was incoherent and rambled to police during an interrogation that lasted deep into the evening. He "really confused things," she said, without elaborating.

Buxbaum said Asim C. had received psychiatric care in the past few years. Investigators said he had no prior criminal record.

Experts were still analyzing the book and a CD or DVD also found in the backpack, Edelbacher said.

The motive for the bombing attempt remained unclear. U.S. Embassy officials did not return telephone messages from The Associated Press seeking comment.

Rather than blow up the backpack in a controlled explosion, a police bomb squad used a water cannon to partially tear it open so the contents could be preserved and examined, officials said.

"There were a lot of nails in that bag. Had it exploded, it would have had an enormous shrapnel effect," Edelbacher said.

Gerhard Jarosch, a spokesman for the Vienna public prosecutor's office, said he expected the men to be transferred to a court in the capital by Wednesday.

He said it was quite clear that Asim C. was "not fully there mentally" and suggested he may be admitted to a special facility while awaiting trial.

Guenther Ahmed Rusznak, a spokesman for Vienna's Islamic community, issued a statement late Monday condemning the incident and rejecting radical Islam.

Last month, authorities arrested three suspected Al Qaeda operatives — all Austrian citizens of Arab origin in their 20s — in connection with a video posted online in March that had threatened Austria and Germany with attacks if they did not withdraw their military personnel from Afghanistan.

One of the suspects was released several days later for lack of evidence. Authorities in Canada, meanwhile, arrested another suspect believed to be linked to the Internet threat.