The German government faces a full parliamentary inquiry into whether members of the foreign intelligence service helped the United States military in the 2003 Iraq war after the opposition liberal Free Democratic Party (FDP) voted in favor of a probe on Monday.

The FDP's decision follows a report in the New York Times last week that German agents handed over sensitive documents detailing Saddam Hussein's defense strategy to the Americans.  

The article caused an uproar in Berlin because it exposed the former government of Gerhard Schröder to accusations of double standards -- gaining popularity among German voters by refusing to back the war in public while privately helping the Americans to wage it.

Officials have warned that a probe, in which current and former officials would have to testify under oath, will put the spotlight on the Germany's foreign intelligence service, the Bundesnachrichtendienst (BND), in the coming months and thereby hamper its activities.

The inquiry could also hurt Chancellor Angela Merkel's government even though she only took over last November because her grand coalition's foreign minister, Frank-Walter Steinmeier of the Social Democrats, was chief of staff to Schröder at the time of the war.

Lengthy debate about the Iraq war and Germany's role in it could also put further strain on US-German relations at a time when Merkel is trying hard to repair the damage done by Schröder's opposition to the war.

Monday's move by the FDP's ends weeks of uncertainty about whether the Bundestag, or lower house of the German parliament, will launch an inquiry. The other two opposition parties, the Left Party and the Greens, had already called for a probe. The FDP's support gives the combined opposition sufficient votes -- a quarter of all deputies -- to force a parliamentary investigation.

The question is now the scope of the mandate the inquiry will be given. The FDP and Left Party want it to comprise the previous government's whole policy during the Iraq war. That would put the inquiry on course to look at a number of sensitive German-US security issues.

These include the alleged abduction of a German national to Afghanistan by the US Central Intelligence Agency, as well as revelations that German security officials questioned inmates at the Guantanamo Bay detention camp for terrorism suspects in Cuba.

The Greens, who were the junior coalition partner in Schröder's government, want a narrower remit focusing on the activities of the BND.

FDP domestic policy expert Max Stadler said: "We don't want an investigating committee against the BND, instead we want a debate about the political responsibility for all that happened and what conclusions to draw from it."

The German government has admitted that its spies passed on information about locations of Saddam Hussein's Republican Guards and of an Iraqi secret service base to the US government.

But Steinmeier reiterated his denial on Monday of the New York Times claim that the BND handed the US a sketch of Iraqi defence installations around Baghdad in February 2003.

Steinmeier told Frankfurter Allgemeine Zeitung that the BND had found no trace of the sketch despite making an intense search. "So I can and must assume that it wasn't passed on by the BND," he told the paper.