Germany's involvement in a military intervention in Syria is "out of question" under the current circumstances, she said last night during the only TV debate with her Social Democrat (SPD) opponent Peer Steinbrueck ahead of the parliamentary election on September 22.
Germany can participate only when there is a mandate from the United Nations, the north Atlantic alliance (NATO) or the European Union, Merkel said.
However, the international community should respond collectively to the alleged use of chemical weapons by the Syrian army, which is a "hideous crime" and a violation of the 1925 Geneva Protocol banning the use of such weapons, she said.
Chancellor Merkel pledged to "do everything" to achieve a consensus at the UN Security Council, which has been deeply divided on how to stop the two and a half year conflict in Syria that has killed an estimated 100,000 people and displaced over a million population.
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She welcomed US president Barack Obama's decision on Saturday to seek congressional authorisation for a military intervention in Syria which effectively rules out a military intervention at least until the US congress reconvenes on September 9.
The chancellor said she intends to raise this issue during her discussions with Russian President Vladimir Putin and Chinese President Xi Jinping on the sidelines of the G-20 summit, which opens in St Petersburg on Thursday and will seek their support for a joint initiative by the UN.
Use of chemical weapons cannot be accepted under any circumstances and the international community should not be divided on such an issue of great importance, she said.
Steinbrueck also spoke against Germany's participation in a western military intervention in Syria and warned the US against launching an attack without a UN mandate.