WASHINGTON (AFP) - A bipartisan group of US lawmakers have urged President Barack Obama and their colleagues to bring an end to the war in Afghanistan, insisting that the killing of Osama bin Laden made the mission unnecessary. The death of bin Laden require us to reexamine our policy of nation building in Afghanistan, said the four Democrats and four Republican representatives in letters to Obama, sent earlier this month, and addressed to colleagues on Wednesday. They said the time has come to acknowledge that the threat posed by Afghanistan no longer justifies 100,000-plus troops on the ground. The group, headed by Republican Jason Chaffetz and Democrat Peter Welch, have made a bipartisan push for an end to the conflict, offering an amendment to a defence bill that would require the withdrawal of US ground troops. In light of the killing of the September 11 mastermind in a May 2 commando raid, the conflict is no longer the best way to defend America against terror attacks, and we urge you to withdraw all troops from Afghanistan that are not crucial to the immediate national security objective of combating Al Qaeda, said the group. Obama has set July 2011 as the start date for the withdrawal of US troops from Afghanistan, and the end of 2014 as the time that US and Nato forces must transfer security responsibilities to Afghan forces. The lawmakers noted the immense cost of the conflict for US taxpayers: $2 billion a week, and $386 billion already spent. They argued that a nation-building strategy in Afghanistan has little efficacy, and that military action should be focused on special forces mission to target dispersed and decentralised extremist groups. With polls showing that much of the US public is tired of the war, the Obama administration has in recent months played down the prospect of a military solution in Afghanistan and called for a political settlement. The lawmakers letter to their colleagues comes a day after Senator Richard Lugar, the top Republican on the Senate Foreign Relations Committee, questioned why the United States was spending some $120 billion a year in Afghanistan. The question before us is whether Afghanistan is strategically important enough to justify the lives and massive resources that we are spending there, especially given that few terrorists in Afghanistan have global designs or reach, the Indiana lawmaker said.