'Small explosion' near US embassy in Montenegro, investigation 'evolving' The embassy in the Balkan nation issued the alert Thursday morning.

 -- There was a "small explosion" near the U.S. embassy compound in Podgorica, the capital of the Balkan nation of Montenegro, at approximately midnight local time Thursday, the State Department has confirmed to ABC News.

"At 00:30, in front of the @USEmbassyMNE building in #Podgorica, #Montenegro an unknown person committed suicide with an explosive device," the government of Montenegro tweeted. "Immediately before, that person threw an explosive device from the intersection near the Sport Center into the US Embassy compound."

A subsequent tweet read, "Most probably, the device was a hand grenade. Police investigation and identification is under way directed by the prosecutor."

"At this time, embassy officials are working closely with police to identify the assailant(s)," a State Department spokesman said.

The spokesman said the investigation is "evolving."

"The embassy is currently conducting an internal review to confirm the safety of all staff," the spokesman added.

Initial reports indicate there was no impact on U.S. personnel, according to the State Department.

On its Facebook page, the embassy said visa services were cancelled on Thursday, and that "American Citizen Services will be available today on an emergency basis."

The embassy had initially announced on its website that it was experiencing "an active security situation."

The warning on the website said the embassy "advises U.S. citizens there is an active security situation at the U.S. embassy in Podgorica. Avoid the Embassy until further notice."

It listed a series of "actions to take," which included avoiding the area around the embassy, monitor local media, avoid large gatherings and demonstrations, follow the instructions of local authorities, and "employ sound security practices."