BERLIN (AFP) German President Horst Koehler announced his surprise resignation on Monday after appearing to suggest the countrys unpopular Afghanistan mission was partly motivated by commercial interests. I am resigning my post as federal president with immediate effect, Koehler, 67, whose job is largely ceremonial but who has to sign legislation before it can become law, said in Berlin. It was an honour for me to serve Germany as president, a visibly emotional Koehler, only a year into his second term, told reporters with his wife at his side. I thank the many people in Germany who have put their trust in me and supported my work. I ask for you to understand my decision. Koehlers resignation creates another headache for the already under-pressure Chancellor Angela Merkel, 55, whose popularity has plummeted barely half a year into her second term. A former managing director of the International Monetary Fund, the popular Koehler was elected in 2004 by MPs and public figures and won a second term in May 2009. Koehler is a political ally of the conservative Merkel, who invested considerable capital in getting him to serve a second term, seeing off a challenger from the centre-left. Koehler came under fire earlier this month for saying that an export-reliant country like Germany occasionally needed to defend its economic interests by preventing regional instabilities like that in Afghanistan. Such regional instabilities certainly have a negative impact on us through trade, jobs and income, Koehler told German radio on May 22. I regret that my remarks about an important and difficult issue for our country could lead to misunderstanding, he said. After the interview, Koehler said his comments were misunderstood and that they were not meant to refer to the mission in Afghanistan, where Germany has around 4,350 troops in a Nato-led force tackling a Taliban-led insurgency. Instead, his office said, the president was referring to operations such as an international mission involving German warships to keep pirates away from commercial shipping off the Horn of Africa. Polls show that a majority of Germans are opposed to the mission in Afghanistan, where German troops are facing an increasingly tenacious insurgency in the north and where 39 troops have died since 2002.