Pakistan police on Saturday raided shanty dwellings in and around Islamabad, rounding up 70 people they said were mostly Afghan refugees.
The raids in Taxila town, some 30 kilometres (18 miles) west of Islamabad and near the capital's airport were aimed at preventing terrorists from entering the city to carry out fresh strikes, police said.
"Seventy people have been rounded up in Taxila and Islamabad as part of a search operation aimed at preventing infiltration of terrorists in the city and neighbouring Rawalpindi," a police official said, requesting anonymity.
He said most of those rounded up were Afghan refugees.
Another police official said police would verify "authenticity of identity papers and other documents of these people," adding that all those with valid documents would be released.
"But action will be taken against those who don't possess valid documents," he added.
During Afghanistan's nearly three decades of civil war and turmoil, large numbers fled their homeland, mainly to neighbouring Pakistan and Iran.
More than five million Afghans have returned home since the fall of the Taliban regime in late 2001, according to the UNHCR.
Pakistan still hosts 1.7 million refugees, most of them in the North West Frontier Province (NWFP) and southern Baluchistan province, a UN refugee agency official told AFP.