Guido Westerwelle
© Reuters//Guido KrzikowskiGerman Foreign Minister Guido Westerwelle.
As tensions mount between Western nations and Syria, the German authorities said Thursday that they had ordered the expulsion of four Syrian diplomats after arresting two men accused separately of spying on opponents of President Bashar al-Assad.

The police here arrested the two men on Tuesday, saying they were "strongly suspected of investigating Syrian opposition members in Germany for a Syrian intelligence service over a period of years."

The men were identified, under standard German procedures, only as Mahmoud El A., 47, of Lebanese descent, and Akram O., 34, a Syrian.

State and federal police officers searched the homes of six other suspects "believed to be involved in espionage," prosecutors said.

In a statement on Thursday, Guido Westerwelle, the German foreign minister, said the four diplomats - three men and a woman who were not identified by name - had been given three days to leave Germany. Mr. Westerwelle did not go into detail about the expulsions, but officials said the embassy personnel were suspected of carrying out activities incompatible with their diplomatic status, a formulation that usually refers to espionage.

The action came after several Western and Arab nations reduced their diplomatic presence in the Syrian capital, Damascus. The United States closed its embassy there this week.

Syrian officials made no immediate public comment on the expulsions.

After Tuesday's arrests, Mr. Westerwelle summoned the Syrian ambassador to tell him that intimidation of Syrian opposition figures in Germany would not be tolerated, officials said. According to German news reports, the two men arrested were not diplomats, but worked closely with Syrian Embassy officials.

Their activities were said to have included infiltrating demonstrations to photograph Syrians opposed to Mr. Assad and then transmitting the images to Damascus along with other information about the government's opponents.

About 32,000 Syrian citizens are registered as living in Germany, according to official statistics, and around 2,600 of them applied for asylum in the 11 months since the Syrian uprising began in March 2011.

Many Syrian exiles have complained of harassment.

Late last year, Ferhad Ahma, a politician of Syrian descent from Germany's opposition Green Party, who is also a member of the Syrian National Council opposition movement, said he was attacked in his apartment.

A statement from the Greens at the time said two men posing as police officers arrived at his apartment at 2 a.m. and beat him with metal bars and clubs when he opened the door. Green Party officials accused Syrian agents of responsibility, but the police said the identity of the assailants was not clear.

The practice of spying on overseas opponents is not restricted to Germany or Syria.

In October, a Syrian-American man was arrested in the United States and accused of secretly working with Syrian intelligence to gather information on overseas protesters. The Syrian Embassy in Washington has called the charges baseless.