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

No one else apparently was hurt and there was no major damage. Police sealed off the area after the blasts around midnight (2300 GMT Wednesday).

"In front of the @USEmbassyMNE building in #Podgorica, #Montenegro an unknown person committed suicide with an explosive device. Immediately before, that person threw an explosive device," the official government account tweeted, adding that the device was "most probably" a hand grenade.

The U.S. State Department said embassy officials were working with police to identify the assailant and was working internally to confirm all staff are safe.

The embassy added that it had canceled all visa services for Thursday, adding that access for U.S. citizens "will be available today on an emergency basis."

A guard at the sports center who asked not to be named said he "heard two explosions, one after another."

"Police came very quickly and the body of a man was taken away," the witness told French Press Agency (AFP).

The heavily secured embassy building is located on the outskirts of Podgorica's city center, near the secret police headquarters and Moraca river.

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.

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.

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