Faced with an increasingly sophisticated insurgency, the US on Thursday said Pakistan was not doing enough to contain attacks on coalition forces in Afghanistan as militants operating from safe havens in its tribal areas have grown “bolder” and more “diverse”.Asking Pakistan put pressure on militant groups, top Pentagon officials also indicated increasing the strength of US forces in Afghanistan.In the aftermath of last week’s attack on the US forces in Afghanistan that left at least nine soldiers dead, Chairman of the Joint Chiefs of Staff Admiral Mike Mullen said foreign fighters from the Pakistani side are moving into Afghanistan “unmolested and unhindered”.Mullen, who was in Pakistan recently, argued that the well coordinated attack on the Wanat outpost in Afghanistan has proved that the enemy has grown “bolder, more sophisticated, and more diverse”.The Bush administration is under tremendous pressure to increase its force levels in Afghanistan.“We’re seeing a greater number of insurgents and foreign fighters flowing across the border with Pakistan, unmolested and unhindered. This movement needs to stop. We simply must all do a better job of policing the border region and eliminating the safe havens, which serve today as launching pads for attacks on coalition forces.”Mullen said “..it’s a more sophisticated group. They’ve been able to train in a safer environment in the safe havens in Pakistan, so that is - it has become a significant contribution, and it’s the freedom of movement across that border.”Criticising Pakistan, Defence Secretary Robert Gates said Islamabad was not putting any pressure on militants who are launching attacks on coalition forces in Afghanistan.