German Foreign Minister Guido Westerwelle said on Thursday Germany was expelling four diplomats from the Syrian embassy in Berlin after the arrest of two men suspected of spying on regime opponents.

"After the arrest of two people suspected of spying for Syria, I have decided to expel four members of the Syrian embassy in Berlin," Westerwelle said in a statement.

"The Syrian ambassador has been informed of this decision," added the minister.

Two men, identified only as 47-year-old German-Lebanese citizen Mahmoud El A. and 34-year-old Syrian national Akram O., were arrested in Berlin on Tuesday.

Westerwelle summoned Syria's ambassador following the arrests.

"The position of the federal government was made unmistakably clear at this meeting that the possible action against the Syrian opposition in Germany will not be tolerated," the ministry said.

In late December, a Berlin local politician active in the Syrian opposition was attacked by two men in his home in a case the German foreign ministry said it was following closely.

The man's party, the Greens, said it suspected the Syrian secret services were behind the assault.

No suspects have been identified in the case.