Bomb disposal experts are investigating two suspect vehicles containing gas bottles near the US embassy in central Brussels, a Belgian Defence Ministry spokesman said.
"As far as I know there are two suspect vehicles, one close to the American embassy and one close to the Belgian Defence Ministry," said ministry spokesman Didier De Weerdt.
"Apparently there are gas bottles inside the vehicles."
He said several buildings had been evacuated between the embassy and the ministry and a bomb disposal squad was assessing the vehicles. Police have closed several of the main routes through the district and out of the city centre.
The US embassy in Brussels was evacuated while police investigate a suspect vehicle, officials and police said.
"I can confirm we have been evacuated. There was a suspect vehicle," said Viktor Sidabras, the spokesman for the US mission to the European Union.
Belgian news agency Belga said police closed several main routes out of the city and sealed off a security zone around the embassy
An eyewitness has told local media that there were a dozen worshippers in the mosque when a man attacked with a petrol bomb. An imam died as a result of smake inhalation, and another person was injured. Azzedine Laghmish told Belgium's national broadcaster RTBF:
A man has been taken into custody following an arson attack on a mosque in the Brussels suburb of Anderlecht, police spokeswoman Marie Verbeke told AFP.
An imam has died after an arson attack on a mosque in the Anderlecht district of Brussels in Belgium. Witnesses said a man entered the mosque before throwing a petrol bomb. Initial reports said the imam, 47, died of smoke inhalation, and one other person was injured.