NATO Secretary-General Jaap de Hoop Scheffer joined the debate on Afghanistan Saturday, increasing pressure on Germany to deploy troops in the hostile south of the country where Taliban insurgency is strongest, according to dpa. De Hoop Scheffer told Bild am Sonntag newspaper that Germany should expand its military activities in Afghanistan, a day after Chancellor Angela Merkel's government rejected calls by US Defence Secretary Robert Gates to do just that. "Germany plays a leading role in the north and is doing an exemplary job. But I believe the International Security Assistance Force (ISAF) could use more of this in other parts of Afghanistan," he said. "I think all nations should show greater flexibility in the deployment of their forces," de Hoop Scheffer said in an interview, excerpts of which were released in advance of publication Sunday. Germany has around 3,200 soldiers serving with the 37,000-strong NATO-led ISAF. Most of them are engaged in training and reconstruction work in the relatively peaceful north. Under a mandate approved by parliament in October, Germany can only send combat troops to the south under exceptional circumstances. In a strongly-worded letter to Defence Minister Franz Josef Jung, Gates asked Germany to consider a new mandate which could allow thousands more troops to be sent to Afghanistan, with some deployed to the more dangerous south. With experts warning of more Taliban attacks, Washington wants the troops to replace the 3,200 Marines it is sending to Afghanistan to beef up the 26,000 US soldiers already stationed there. The Marines, though, are only supposed to stay for seven months at the most, after which other NATO allies are expected to provide replacements. Gates warned that without reinforcements NATO faced a loss of credibility and a division within the alliance, according to sources who have seen the letter. The reluctance of allies like Germany and France to make more troops available for a combat role has frustrated the US, Canada, and other NATO allies whose troops have been taking losses fighting the Taliban and al-Qaeda. Canadian Prime Minister Stephen Harper issued a warning earlier this week that Canada might end its military mission in the dangerous south unless other NATO countries send more troops. German politicians are reluctant to commit more forces amid growing concern among the population that the country could become a target for terrorists because of its involvement in Afghanistan. Jung rejected Gates' call for more combat troops to be sent to the south and said Germany would continue to concentrate on its reconstruction efforts in the north. "We have agreed on a clear division of labour," Jung said. "I believe that we really need to keep our focus on the north." De Hoop Scheffer described Gates' letter as "unhelpful," a view shared by many German politicians. "We need to do more but it doesn't help to go public about this," he said. "Such an approach will conceal the gains we have already made in Afghanistan." Opposition Greens Party defence spokesman Winfried Nachtwei said the tone of the Gates letter was a "relapse" into the era of former defence secretary Donald Rumsfeld. "The German government should not allow itself to be blackmailed by a sinking US administration," he said. Germany has been considering a NATO request for combat troops for a Quick Reaction Force in northern Afghanistan to replace a 350- strong Norwegian force that leaves in July. Government sources said the defence ministry would probably agree to the request.