Afghan police tightened security in the southern city of Kandahar on Sunday as officials searched for an American aid worker, her Afghan driver and their kidnappers.

No group had yet claimed responsibility for seizing Cyd Mizell or the driver, Abdul Hadi. Gunmen kidnapped the two on Saturday in a residential neighborhood of Kandahar.

Mizell, who was wearing the all-encompassing burqa that many Afghan women wear when she was taken, works on aid projects for the Asian Rural Life Development Foundation. The director of Mizell's aid organization, Jeff Palmer, said the kidnappers hadn't contacted officials.

"We are trying our best to find them," provincial Gov. Asadullah Khalid said.

Several foreigners — including 23 South Koreans, two German construction workers and two Italian journalists — have been kidnapped in Afghanistan in the last year, but kidnappings of Americans are rare. An American civilian was briefly abducted in Kabul in April 2005 but escaped by throwing himself from a moving car.

Abdul Mahdi, the brother of Hadi, the driver, said his family was upset because the police still hadn't contacted them to ask questions. He described his brother — a 35-year-old with five children — as the "most trustworthy" driver the Asian Rural Life Development Foundation had.

"All the children couldn't sleep last night after learning their father had been taken," Mahdi said. "And we are upset that the police haven't come to the house to ask us anything."

Mizell taught English at Kandahar University and gave embroidery lessons at a girl's school, and she speaks the local language, Pashtu, well, colleagues said. Palmer said she has worked for ARLDF on income-generating women's projects in Kandahar for the last three years.

Traveling around Kandahar city has turned increasingly dangerous in the last year, as the Taliban insurgency has spread throughout southern Afghanistan.

Western civilians who operate there often travel with armed guards and extreme caution. The area is rife with Taliban militants and criminals linked to the country's booming opium poppy trade.

Kidnappings for ransom are an increasing problem in Afghanistan. Dozens of Afghans have been abducted in the last year, and heavy rumors persist nationwide of foreign governments paying large ransoms to win the freedom of their citizens. Two of the 23 South Koreans kidnapped in July were killed.

In violence, a soldier in NATO's International Security Assistance Force died after being hit by gunfire during a patrol in Nuristan province in eastern Afghanistan. Most soldiers in the east are American, though NATO didn't provide the soldier's nationality.

In the Panjwayi district of Kandahar province, two police were killed by a roadside bomb, said Haji Baran Khan, the Panjwayi district chief. Their police vehicle was destroyed, he said.