WASHINGTON/KUNDUZ (Reuters/AFP) A US-led offensive in southern Afghanistan moved at a cautious pace Thursday as allied troops sought to spare civilian casualties and avoid numerous roadside bombs planted by the Taliban. The squeeze is being put to the Taliban, said Pentagon spokesman Geoff Morrell in Washington, adding the United States was pleased with the rate of progress despite the threat posed by a slew of bombs planted across Marjah. NATO and Afghan troops have hit pockets of stiff resistance as they assault the Talibans main stronghold in southern Afghanistan and may need another month to secure the area, a NATO commander said on Thursday. Major General Nick Carter, the British commander of NATO forces in southern Afghanistan, said the military operation in Marjah, located in Afghanistans most violent province of Helmand, was at the end of the beginning. The assault, launched almost a week ago, is meant to create a sense of momentum that will sweep eastwards towards Kandahar (in) the course of the next six months, he told reporters at the Pentagon, referring to the biggest population center in southern Afghanistan. Carter, speaking by video link from Afghanistan, cautioned it would take up to another month to fully clear the Marjah area and about three months to get a pretty fair idea about whether weve been successful. As NATO and Afghan forces increase pressure on Taliban fighters in and around Kandahar, Carter said insurgents were likely to turn increasingly to asymmetric tactics, such as suicide bombings. Carter said he was satisfied with the pace of operations but that progress was slow and steady due to the threat posed by mines and other explosive devices left by the Taliban. In Marjah itself there remains stiff resistance from the insurgents, he said. It will be some days before we can be completely confident that Marjah is secure. I guess it will take us another 25 to 30 days to be entirely sure that we have secured that which needs to be secured, and we probably wont know for about 120 days whether or not the population is entirely convinced by the degree of commitment that their government is showing to them, he said. Carter acknowledged it was too early to say how the population will respond. Meanwhile, a NATO airstrike mistakenly killed seven Afghan police and wounded two others on Thursday, hospital and government officials said, adding to strains on the alliance. The NATO-run International Security Assistance Force ordered an immediate investigation into the incident in the northern province of Kunduz, where Taliban violence has recently increased, and hailed the role played by Afghan forces. The incident occurred when a joint patrol by the Afghan army and police and NATO forces came under Taliban attack in the Imam Sahib district, Afghan interior ministry spokesman Zemarai Bashary told AFP. NATO called in an airstrike and the Afghan forces were bombed by mistake, the spokesman said.