The Green Party, which the victim Ferhad Ahma represents on a Berlin district council, suspected the Syrian secret services were behind the assault early Monday, according to the party's chief whip in the national parliament, Volker Beck.
Ahma suffered serious bruises and other wounds in the attack but declined medical treatment, police said.
The Greens said in a statement that two men claiming to be policemen arrived at Ahma's flat at around 2 am and when he opened the door, began beating him with metal bars and clubs.
The party said the men's Arab appearance as well as the fact that Ahma had been threatened before led it to conclude the attackers were linked to the regime in Damascus.
Beck called on Foreign Minister Guido Westerwelle to summon the Syrian ambassador over the attack and on German authorities to assure Ahma's safety.
"It is unacceptable that a member of the Syrian opposition can be hunted, persecuted and intimidated in Germany by the Syrian services," Beck said.
A foreign ministry spokeswoman said it was aware of the assault on Ahma "and the accusations against Syria in that context."
"(The ministry) is in contact with the relevant investigating authorities and made clear its interest in a quick and comprehensive clarification of what occurred," she said.
A spokesman for the Berlin police said that its state security force had taken over the investigation but that it was still unclear who was behind the attack.
The foreign ministry said Thursday it had summoned Syria's ambassador to Berlin to demand an immediate halt to the "brutal" repression of anti-regime demonstrators by government forces.
The United Nations says more than 5,000 people have lost their lives in nine months of bloodshed.