KABUL (Agencies) - Insurgents killed two US troops in Afghanistan on the anniversary of the 9/11 attacks, making 2008 the deadliest year for American forces since US troops invaded the country in 2001 for sheltering Osama bin Laden, according to the International Herald Tribune. The deaths brought the number of troops who have died in Afghanistan this year to 113, according to an American news agency tally, surpassing last year's record toll of 111. Afghanistan was the launching pad for Al-Qaeda's terrorist attacks on Sept 11, 2001. US forces invaded in October 2001 in response and quickly drove the Taliban out of power. Across Afghanistan, US troops paused in silence Thursday to commemorate the 9/11 attacks. At a US base in Kabul, members of the New York National Guard, many of whom served at the site of the World Trade Centre after the towers came down, remembered the attack on their home state. Osama bin Laden, leader of the Al-Qaeda network, is believed to be in the tribal belt on the Pakistan-Afghanistan border. He had been sheltered by Taliban leader Mullah Omar before 9/11. Taliban fighters folded in easy defeat in fall 2001 in what at first appeared to be a resounding US victory. But militants that US commanders once derided as ragtag amateurs have transformed into a fighting force advanced enough to mount massive conventional attacks. Suicide and roadside bombs have turned bigger and deadlier than ever. The number of Arab, Chechen and Uzbek militants flowing into the Afghan-Pakistan region has increased this year, bringing with them command expertise the Taliban lacked. US death tolls have climbed sharply from the first years of the war. Only five American service members died in 2001. Thirty service members died in both 2002 and 2003; the toll climbed to 49 in 2004, then 93 in 2005 and 88 in 2006. Last year 111 troops died, including one killed by a sniper while meeting with Pakistani officers in Pakistan. That mark was surpassed Thursday - with more than three months left in the year - reflecting both the increased number of American troops deployed to Afghanistan as well as the insurgency's increasing potency. Top US generals, European leaders and analysts say the blame lies to the east, in militant sanctuaries in neighbouring Pakistan. As long as those areas remain havens where fighters arm, train, recruit and plot increasingly sophisticated ambushes, the Afghan war will continue to sour. "Even in areas where there is no substantial fighting, the presence of insurgents has increased," said Anthony Cordesman, a security expert with the Washington-based Centre for Strategic and International Studies. "You have less cooperation from Pakistan, and there's political disarray," which creates a situation where there is little security and stability, Cordesman said. Since the 2001 invasion, a total of 519 US troops have died in the Afghan war, including those killed in border areas of Pakistan and in Uzbekistan, which was a staging area in 2001. Some 33,000 US troops are now stationed in the country, the highest level since 2001. Overall, more than 65,000 troops from 40 nations are deployed in Afghanistan. US commanders in Afghanistan say they need another 10,000 troops - even more than a deployment plan announced by US President George W Bush this week. The commanders also urge more non-military aid and say the Afghan government must perform better. Adm Mike Mullen, chairman of the Joint Chiefs of Staff, told the House Armed Services Committee this week that, "I'm not convinced we're winning in Afghanistan. I'm convinced we can."