The online portal of German news outlet Spiegel on Friday reported that the foreign ministry had issued the request to embassies in Berlin on Wednesday.

Spiegel reported that the request to provide a list with the names of all active secret service agents came in the form of a "note verbale" or third-person note. The request reportedly also calls for the names of staff at consulates, cultural institutions and the secret services. According to the report, the foreign ministry expected its non-binding but formal note "to be answered by all the recipient agencies."

German relations with the US were already strained by the issue of espionage last year, when reports suggested that the US National Security Agency (NSA) had tapped the mobile phone of Chancellor Angela Merkel and her predecessor, Gerhard Schröder.

More recently, employees from Germany's NSA-equivalent Bundesnachrichtendienst (BND) and the German defense ministry came under suspicion as potential "double agents" also working for the US. Germany asked the top CIA officer at the US embassy in Berlin to leave the country last month.

According to Spiegel, the government's unusual diplomatic request was the upshot of frustration at Washington's reticence to name at least the secret service personnel officially posted in Germany. The report said that the message - written on foreign ministry letterhead as it is addressed to foreign embassies - was approved by all relevant ministries and the chancellery.

Domestically, the German interior ministry is in the process of improving its counter-espionage procedures in light of the revelations from former NSA contractor Edward Snowden. Some 3,000 federal government staff have already received encrypted mobile or cell phones, and Berlin is also mulling expanded counterintelligence measures - including monitoring allies in the country.

msh/jr (AFP, dpa)