ATHENS (Reuters) - Gunmen set fire to Microsoft's Greek headquarters in Athens overnight, police said on Wednesday, damaging the front of the building and forcing the U.S. software firm to suspend its operations in the city.

"The van contained three inflammable gas canisters and five cans of gasoline," a police source said.

The ground floor of the building suffered damage and the van was completely destroyed in the attack, which was carried out by at least two people and took place at about 0145 GMT.

"There was extensive damage on the ground floor. Microsoft will not operate today," police spokesman Thanasis Kokkalakis said.

(Reporting by Harry Papachristou; Editing by John Stonestreet)