Afghan authorities and people of southern Afghanistan say they are witnessing an upsurge in suicide attacks.
They blame Pakistan for failing to stop an influx of Taliban fighters.
But there are vast tracts of land between Pakistan and Afghanistan where border control barely exists.
Nato is speaking out against a peace deal between the Taliban and the Pakistani government.
The organisation says the truce in the North-West Frontier Province has already led to a rise in violence across the border in Afghanistan.
In a rare news conference, the Taliban's leader in Pakistan, Baitullah Mehsud, vowed to keep sending suicide bombers to kill US troops in Afghanistan.
Al Jazeera's Teresa Bo reports from the Afghan town of Spin Boldak, on the historic issues that make border policing difficult.