The president of the European Parliament on Monday condemned all forms of political violence during a visit to Athens, after the murders of two members of a Greek neo-Nazi party and a left-wing rapper.

"I condemn those who kill people no matter what the reason is. There is no political justification for murder," Martin Schulz said.

"[This kind of violence] is a sign of alarm and destabilisation," he added.

Schulz called for "mutual respect, even from parties which deny respect and dignity."

"These parties exist. In a democracy we do not fight them with violence but with arguments," added Schulz, who chaired an EU parliament conference on the economic prospects of Europe's south.

On Friday, two armed assailants riding a motorbike shot dead two members of the Golden Dawn party and seriously injured a third one in a shock drive-by attack outside the party's offices in an Athens suburb.

Experts fear this could lead to an increase in violence, as the attack followed the assassination in mid-September of an anti-fascist rapper by a Golden Dawn member.

"Those who vote for extremist parties are not dedicated Nazis, they are people in despair," Schulz said.

So far no one has claimed responsibility for the double murder and Greece's anti-terrorist squad is searching for the assailants who remain unidentified.

Local television channels screened a video obtained from nearby surveillance cameras, which is in the hands of the police.

In the video, panic reactions can be heard coming from those who witnessed the attack, which occurred in a busy street early on Friday evening.

The funerals of 22 year-old Manolis Kapelonis and 27 year-old Giorgos Fountoulis took place on Monday.

Fountoulis' family requested that no politicians attend the funeral.