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PODGORICA, Montenegro — An attacker threw a hand grenade at the U.S. Embassy in Montenegro's capital and then killed himself with another explosive device, officials said Thursday.

Police guard the entrance to the U.S. Embassy in Podgorica, Montenegro, on Thursday. Boris Pejovic / EPA

No one else apparently was hurt and there was no major damage. Police sealed off the area after the blasts around midnight local time (6 p.m. ET Wednesday).

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The State Department said embassy officials were working with police to identify the assailant and was seeking to confirm that all staff were safe.

Police officers armed with submachine guns were out on the streets near the building on Thursday morning.

U.S. citizens were advised to stay away from the embassy until further notice and visas were not being issued on Thursday.

Montenegro borders the Adriatic Sea in southeastern Europe and its capital is Podgorica. It joined NATO last year despite strong opposition from its traditional Slavic ally Russia.

A map showing Montenegro. Bing Maps

Several people, including two Russian secret service operatives, are on trial in Podgorica on charges that they wanted to overthrow Montenegro's government in 2016 because of its pro-Western policies.

Montenegro is the smallest of all former Yugoslav republics.

The U.S. established diplomatic ties with the tiny Balkan state in 2006 after it split from much larger Serbia.