Pakistani authorities in the southern city of Quetta have arrested more than 500 illegal Afghan migrants, some of whom, police say, are fugitive militants.
Police in Quetta say they have taken 556 undocumented Afghans into custody during a week-long, city-wide sweep.
Of those arrested, officers have questioned and sent more than 100 back to Afghanistan. Many of those still being held are under investigation as possible militants loyal to Afghanistan's former Taleban government.
The Taleban, along with allies including members of the al-Qaida terror network, have been waging an anti-government insurgency across the eastern half of Afghanistan.
Quetta Police Chief Shoaib Suddle says he suspects the illegal migrants include a significant number of Afghan insurgents, who have been hiding out in the southern city, about 50 miles from the border.
He says his department has passed on the photographs and fingerprints of some suspects to Afghan and Pakistani intelligence.
Many Taleban fighters are ethnic Pashtuns, who usually dress in traditional clothing, but Chief Suddle notes that most residents of Quetta fit this same description. Without outside assistance, police have little chance of determining who are insurgents and who are not.
"If no such information is available, and the only thing is that you have a person, who is speaking a certain language and a dialect, or having a beard or a turban and so on and so forth, it becomes very difficult," he said.
Still, he says there is reason to believe those now in custody include a sizable number of militants.
"We are sharing these photographs with the intelligence agencies, with the Afghan authorities, and the confirmation has to come from their side," said Shoaib Suddle. "But we definitely suspect that, yes, many of them are from that category."
Afghanistan's government, and some Western officials, have previously criticized Pakistan for not doing enough to track down Afghan militants hiding out on its territory, allegations that Pakistan disputes.