Main Greek ruling party New Democracy's headquarters were attacked by gunfire early Monday amid increasing violence against political and media targets across Athens.

No injuries reported so far. Preliminary investigations by police and counter-terrorism units showed that two motorcyclists fired at least nine times with Kalasnikov AK 47 rifles at the building in central Athens, government spokesman Simos Kedikoglou said.

A bullet has been found inside the office of Prime Minister Antonis Samaras, who is head of the conservative New Democracy party, he told state television NET.

Kedikoglou strongly condemned the "fresh attack against our democracy," noting that "the government will do what is required to protect democracy."

The attack came after a series of assault against political parties' offices and homes of journalists since Friday.

An anarchist group has claimed responsibility for the first string of attacks with gas cannisters thrown at homes of five Greek journalists across Athens on Friday.

The group claimed that the media outlets "represent a corrupted political and financial system which has led to the current debt crisis."

During the weekend, a dozen offices of New Democracy, co-ruling socialist PASOK party and main opposition SYRIZA party were firebombed.

On Saturday night, petrol bombs were thrown at the Athens home of the brother of the government spokesman when George Kedikoglou was inside with his wife and a three-year-old child, causing minor damage but no injuries.

The three-party coalition government, consisting of New Democracy, PASOK and Democratic Left, has strongly condemned the attacks, calling on all political parties to take a similar stance.