Austrian police say they have arrested a man who attempted to enter the US embassy in Vienna with a bag containing explosives and nails.
Experts are trying to determine if the devices could have exploded
The suspect is a 42-year-old man of Bosnian origin from the north-eastern province of Lower Austria, police spokeswoman Michaela Raz said.
He was arrested shortly after running off when his backpack triggered a metal detector at the embassy's entrance.
Nobody was injured in the incident, but police sealed off the area afterwards.
Nearby bus and tramway lines were also re-routed. Police are also patrolling the area with bomb-sniffing dogs.
The suspect was caught by police at around 1200 (1000 GMT) not far from the embassy, which is situated on Boltzmanngasse street in the capital's 9th district.
Doris Edelbacher of Austria's federal counter-terrorism office said the explosives found inside his bag resembled grenades, but that explosives experts were still trying to determine whether the devices could have been detonated.
"There were a lot of nails in that bag. Had it exploded, it would have had an enormous shrapnel effect," she told the Associated Press.
The backpack also contained a book in which a reference to Islam appeared, but she said it was not clear whether the attempted attack had an Islamic background.
Ms Edelbacher said the suspect spoke broken German and had for now only made "confused statements" whilst being questioned.
Last month, Austrian authorities arrested three people of Arab origin in connection with a video posted online that threatened Austria and Germany with attacks if the two countries did not withdraw their military personnel from Afghanistan.
The arrests came two days after a telephone bomb threat triggered an alert at a US air base at Spangdahlem in Germany.