Investigators work at the site where former lawmaker of the Russian State Duma Denis Voronenkov was shot dead in Kiev, Ukraine on March 23, 2017. (Xinhua/Sergey)

KIEV, June 8 (Xinhua) -- An explosion occurred in the U.S. Embassy compound here early Thursday, but no one was injured, Ukraine's National Police said.

The blast took place after an unknown assailant threw an unidentified explosive device into the diplomatic mission's premises shortly after midnight local time (around 2100 GMT, Wednesday), the police said in a statement on its website.

The Ukrainian government is investigating the incident as a "terror act," the statement said.

In March, the Polish Consulate in Ukraine's western city of Lutsk was attacked by unidentified assailants, causing no casualties.