Pakistani authorities say they are questioning about a dozen people in connection with the kidnapping of a U.N. refugee agency official.

A Pakistani police official examines the spot and vehicle of where U.N. officials were kidnapped in Quetta, Pakistan, 02 Feb 2009

Pakistani officials say they do not have a clear idea who abducted American John Solecki Monday in the city of Quetta because of the area's high number of criminal gangs, Taliban insurgents and separatist rebels.

No group has claimed responsibility for the ambush. Solecki's driver was killed in the attack.

Authorities have increased security along the Afghan border to prevent the kidnappers from taking the U.N. official to Afghanistan.

Hundreds of people have died in violence in southwestern Pakistan since an insurgency erupted in late 2004. Rebels in the area demand political autonomy and a greater share of profits from the region's natural resources.

In another development overnight, in the country's northwest, Pakistani officials say suspected Islamist militants blew up a bridge serving as a key supply route for NATO forces in Afghanistan.

Officials say they have stopped all traffic on the 30-meter iron bridge and are not sure when they will be able to open the bridge for travel.

Separately, Pakistan's military says its troops have killed at least 35 insurgents in the northwestern Swat valley.

In a statement Tuesday, Pakistani officials say the army targeted militants in an overnight operation in the Khawaza Khela part of the valley.

Militants in Swat are battling to impose a strict interpretation of Islamic law in the one-time tourist haven. A Taliban leader has told families there that girls will be killed if they attempt to go to classes when schools reopen next month. 

Some information for this report was provided by AFP, AP and Reuters.