ROME, Feb 26: A small bomb exploded near the Interior Ministry in Rome on Tuesday, damaging several vehicles, blowing out windows and ratcheting up tension in a city on edge after the threat of an attack on the US embassy.

The blast occurred in a side street by the ministry, destroying a motor scooter and damaging other cars parked nearby. There were no injuries.

Interior Minister Claudio Scajola called it an assault on state security and the blast sparked a war of words between government figures and opposition groups.

Conservative Prime Minister Silvio Berlusconi said recent mass demonstrations by leftist opposition groups had heightened political tension.

“(The explosion) is worrying...I think the political tension needs to be lowered,” Berlusconi told reporters.

The bomb came a week after police arrested four Moroccan men in possession of a tourist map circled with the US embassy, maps of utility tunnels around the diplomatic mission, and a potentially lethal cyanide compound.

A senior source close to that investigation said there was no indication the blast was linked to the embassy probe but Scajola said the attack was very worrying.

“This is a very serious act carried out against the symbol of the state’s security and that of its citizens,” Scajola said, referring to the ministry building.

The blast was heard across the centre, shattering windows and sending residents into the streets before police arrived.

WAR OF WORDS: In a country where politically-motivated bombings by the extreme right and extreme left were rife in the 1970s and 1980s, the blast quickly became a political football.