Gunmen set fire to Microsoft's Greek headquarters in Athens overnight, police said today, damaging the front of the building and forcing the US software firm to suspend its operations in the city.

"The van contained three inflammable gas canisters and five cans of petrol," 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 1.45am.

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

Arson attacks against banks, foreign firms and local politicians have become more frequent in Greece in recent years as the country battles soaring unemployment and struggles through a recession deepened by austerity policies imposed by foreign lenders.

Previous assaults have been mostly blamed on left-wing extremist groups, but police said it was too early to say who was behind Wednesday's attack.

The van, which contained three inflammable gas canisters and five cans of petrol, was completely destroyed while the ground floor of the U.S. software firm's office suffered heavy damage, police said.

Microsoft said it would shut its office in the city while it assessed the damage.

"Staff were told not to come to work today, and probably also tomorrow," the company's spokeswoman Lia Komninou said on Skai TV.

The fire brigade estimated the damage at about €60,000.

In February, a small bomb was left on an empty subway train in Athens, which a far-left group fighting the austerity policies later claimed responsibility for.

Growing public anger at the impact of the austerity measures was reflected in two parliamentary elections in May and June, in which parties opposed to the terms of the country's international bailout performed strongly.

Reuters