An unknown man blew himself up early on Thursday outside the US Embassy building in Montenegro's capital, Podgorica, according to a statement from the Police Administration of Montenegro.

"At 00:30 [23:30 UTC], in front of the US Embassy building in Podgorica, Montenegro, an unknown person committed suicide with an explosive device. Immediately before, the person threw an explosive device from the intersection near the Sport Center into the US Embassy compound," read a tweet on the government's official Twitter account.

The tweet then went on to say: "Most probably, the device was a hand grenade. Police investigation and identification is underway directed by the prosecutor."

Local media said residents heard two explosions in the area around midnight.

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Watch video 00:22 Montenegro: Tight security at US embassy after grenade incident

The news site Portalanalitika.me cited witnesses as saying that police arrived quickly on the scene and sealed off the nearby Boulevard of the Revolution, close to the embassy.

Portalanalitika said the motive for the attack was not yet known.

The embassy warned US citizens to stay away from the area until further notice and told them to monitor local media for updates.

"The US Embassy in Podgorica advises US citizens there is an active security situation," it said on its website.

The New York Times cited Steve Goldstein, the US State Department's undersecretary for public diplomacy and public affairs, who said the building was not damaged and no one at the embassy — which was closed for the night — was hurt.

Montenegro, the smallest former Yugoslav state apart from Kosovo, became part of the nation of Serbia and Montenegro before declaring independence in 2006.

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Last year, it became the 29th country to join NATO.

mm/sms (AP, Reuters)

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