ATHENS, Greece - A hand grenade attack outside the French Embassy in central Athens slightly wounded a policeman early Thursday, police said, days before outgoing U.S. President Barack Obama is due to visit the Greek capital.

Authorities said the policeman, who had been on guard outside the embassy, was wounded when unknown assailants threw a hand grenade outside the embassy building, located opposite Parliament on a major avenue.

Police shut down the area to vehicles and pedestrians for several hours while anti-terrorism forensics experts combed the scene for evidence.

The government condemned the attack and described it as an act of terrorism, adding that the police would track down the culprits.

"The relations of friendship and solidarity between Greece and France can't be affected in the slightest by such terrorist acts," government spokesman Dimitris Tzanakopoulos said in a statement released by his office.

Greece has a history of domestic militants who periodically carry out bomb or shooting attacks against authorities, diplomatic locations or businesses. There was no immediate claim of responsibility for Thursday's attack, and it was unclear why the French Embassy was targeted.

Police said the attack was apparently carried out by two people on a motorbike. A bike matching the description was later found in a central Athens neighbourhood popular with anarchists and was being examined to determine whether it was the one used in the attack.

Authorities said it appeared the policeman had only been slightly wounded because he had been inside an armoured guard post outside the embassy entrance.

The attack came days before Obama arrives in Athens on Nov. 15 for an expected overnight visit. Left-wing organizations have announced they will hold protests during Obama's stay.

The U.S. has frequently been regarded with misgivings in Greece, in part because of Washington's supportive stance during the military dictatorship that ruled the country from 1967-1974.