MARJAH (Reuters/AFP) - US Marines leading one of NATOs biggest offensives against the Taliban in the eight-year war are facing fierce resistance in some areas, including heavy gunfire, snipers and booby traps, US officials said on Monday.Marine units have tried twice since Sunday to reach a bazaar in Marjah, the last militant stronghold in the countrys most violent province, Helmand, only to be pushed back. Coming under heavy gunfire and sniper attacks with one assault lasting over an hour they were forced to call in Harrier jets and attack helicopters with Hellfire missiles. There have been conflicting assessments of how much progress NATO has made but one thing seems clear: the campaign to seize insurgent-held areas ahead of a planned 2011 troop drawdown could drag on for weeks. We are making steady progress, but being very methodical about detecting and clearing routes in an area heavily saturated with IEDs, Marine Capt Abraham Sipe told Reuters in response to an e-mail. Afghan officials said on Sunday that as many as 35 militants had been killed in the first two days of the offensive. In a statement on the groups website, Taliban spokesman Qari Mohammad Yousuf, citing reports from Helmand, said fighters pushed back attacks by NATO troops on Monday. NATO rockets killed 12 civilians on Sunday, the second day of a drive to impose Afghan authority on Marjah, an area of farmland criss-crossed by canals, a breeding ground for insurgents and lucrative opium poppy cultivation, which Western countries say funds the insurgency. Helmand Governor Gulab Mangal said 3 would-be suicide bombers were gunned down on Sunday while trying to blow themselves up among troops. Meanwhile, Afghanistans military said Monday that US-led troops had almost taken control of Taliban bastion Marjah. So far at least nine Afghan civilians and two NATO soldiers have been killed in Operation Mushtarak. Five British and American soldiers have died elsewhere in southern Afghanistan since the assault began Saturday. An AFP photographer on the outskirts of Marjah said troops had advanced painstakingly, coming under Taliban fire and hunting for bombs on Sunday, as they sought to reassure residents that they were in the area to stay. Speaking to AFP behind the front line in the provincial capital Lashkar Gah, a senior Afghan general claimed troops had captured nearly all the targeted territory in the Marjah and Nad Ali areas of Helmand. In Kabul, General Mohammad Zahir Azimi, the defence ministry spokesman, told AFP: Marjah has been almost cleared and our forces are in control. But asserting government control is an enormous challenge in Helmand, provincial Governor Mohammad Gulab Mangal said three out of 13 districts were outside official control. Meanwhile, Afghan police said Monday that an anti-Taliban operation in the Bakwa district of Farah province had killed 27 militants. A British soldier was killed in southern Afghanistan, officials said Monday. The soldier was not part of Operation Mushtarak.