Critics say it is too costly to be practical and just Pakistan's way of deflecting attention from a failure to crack down on Al-Qaeda and Taliban rebels.
But Pakistan insists it is serious about a proposal to erect a huge fence along parts of its rugged and highly porous 2,400-kilometer border with Afghanistan.
President Pervez Musharraf, a key US ally, floated the idea for the barrier during a meeting with US Secretary of State Condoleezza Rice in New York on Monday.
The proposal follows months of fingerpointing by Afghan and US officials at Pakistan's alleged failure to rein in militants operating from its lawless tribal areas.
The criticism has become stronger due to an upsurge in violence in areas near the Pakistani border in the run-up to Afghanistan's parliamentary polls on Sunday. The country's ousted Taliban rulers have vowed to disrupt the poll.
But while Pakistan is keen to show its commitment, Kabul's first reaction to the proposal was unfavourable - mainly because of a dispute over the Durand Line, a boundary between the countries drawn during British colonial rule.
Before talking about building a fence, the two countries should first address "border issues," Afghan interior ministry spokesman Lutfullah Mashal said in Kabul.
In the meantime Afghan foreign ministry spokesman Naved Moiez said the fence would not stop infiltration, the AFP reports.