Unidentified gunmen on Monday kidnapped a US national working for the United Nations refugee agency in Pakistan's south-western province of Balochistan, police said, dpa reported.
The kidnappers intercepted the vehicle of the local head of the United Nations High Commissioner for Refugees, John Solecki, soon after he left his residence in the provincial capital, Quetta, senior police officer Wazir Khan Nasir said.
"The gunmen bundled Solecki into the back of their car and sped away," Nasir said.
The UN vehicle had ploughed into the wall of a house after its Pakistani driver Syed Hashim was shot by the attackers. He later died at hospital.
The UN office in Islamabad confirmed the incident and conveyed "the extreme shock and dismay felt by the whole UN community."
"We strongly condemn this attack on humanitarian workers in Pakistan who have been doing their utmost to deliver their humanitarian mission," a UN statement said. "The United Nations is now taking all possible measures to secure the release of Solecki."
Pakistan's Foreign Minister Shah Mahmood Qureshi strongly condemned the killing and kidnapping as an "unfortunate and dastardly terrorist act."
"The Government of Pakistan is taking all necessary measures for safe and early recovery of Mr Solecki," he said.
No group claimed responsibility. Police official Nasir said agents were examining evidence to find possible leads and had intensified checks on routes leading out of the city.
In Washington, the US State Department said it was looking into reports of the kidnapping, but could not confirm the victim's identity as an American.
Attacks on foreign diplomats and aid workers have increased in recent months in Pakistan.
Suspected Taliban militants are still holding Afghan Ambassador-designate Abdul Khaleq Farahi and Iranian Commercial Attache Heshmatollah Attarzadeh in captivity. Both were abducted late last year.
Taliban are also suspected of kidnapping a Polish citizen who was working for an oil exploration firm.
All those incidents took place in North Western Frontier Province, where Islamic militants have gained control over large areas. Queta, which is near the Afghan province of Kandahar, is also believed to be a hotbed of Taliban and al-Qaeda activities.
United Nations overhauled its security procedures following the September suicide bombing at Islamabad's Marriott hotel, and ordered its international staff in Pakistan to evacuate their families to their home countries.
The Marriott bombing, one of the deadliest in the country, killed 53 people and injured more than 250, including a Czech ambassador, two US marines and a Danish intelligence officer.