Unknown attackers set fire to eight banks, an insurance office and several cars early on Thursday in apparently coordinated strikes throughout the Greek capital, causing damage but no injuries, police said.

The attackers, using camping gas canisters and petrol in their home-made explosive devices, set fire to banks from Piraeus to the northern suburbs, an insurance company office and vehicles belonging to state agencies and security firms.

"It all took place in just 10 or 12 minutes around 2.10 a.m. (12:10 a.m. British time) with calls coming in across the city of minor explosive devices damaging banks and cars," a police official told Reuters.

Dozens of small self-styled anarchist and leftist fringe groups regularly attack banks and government buildings causing minor damage. The attacks have increased in frequency in recent months.

Police said no one had yet claimed responsibility.