U.S. and Afghan forces seeking three kidnapped U.N. workers raided two houses in downtown Kabul (search) on Monday, smashing through walls and doors to detain 10 people and question residents on whether they had seen the missing foreigners.

The top American general in Afghanistan (search) urged a hard line against the kidnappers, whose identity remains unclear, but there was no sign the pre-dawn operation brought the hostages any closer to freedom.

Most of the detainees were later released, an Afghan intelligence official said on condition of anonymity.

Security forces began the assault in the west of the city at about 4 a.m., using rockets to blast a hole in a wall surrounding the two-story home of a doctor working for the United Nations (search), witnesses said.

The doctor, Munir Mosamem, and his 17-year-old son were detained, Mosamem's wife, Zakia, told The Associated Press. The intruders searched the house and confiscated three mobile phones and part of a computer, she said.

U.N. spokesman Manoel de Almeida e Silva said the doctor worked at a clinic for the world body in the city, but had no details on why the man was targeted.

Another eight men were detained in a derelict house next door, where several impoverished families of recently returned refugees were living, witnesses said.

The intelligence official said those eight were quickly released, but that the doctor and his son remained in American custody.

A woman who gave her name as Angoma, 28, said her husband was among those taken away, with his hands bound and his head covered by a hood.

"They showed us pictures of the three hostages, two women and one man, and asked if we had seen them," she said. "I told them I recognized them from the television, but we don't know anything about them or where they are."

An elderly woman called Mabuba, sharing the doctor's house, also said she was questioned on whether she knew where they were.

"I told them no, and that we are very sad about this case," she said.

Lt. Col. Pamela Keeton, a spokeswoman for the American military, said the joint operation was "related to the hostage situation." U.S. officials declined to elaborate.

Armed men seized Philippine diplomat Angelito Nayan (search), British-Irish citizen Annetta Flanigan (search) and Shqipe Hebibi (search) of Kosovo in Kabul on Oct. 28, the first such abduction in the Afghan capital since the Taliban fell three years ago.

Afghan officials believe a criminal gang carried out the abductions, and that negotiations have centered on a ransom demand. But it remains unclear if the kidnappers are working for a Taliban-linked group that has claimed responsibility and demanded that Afghan and U.S. authorities free jailed comrades.

The leader of the group, which calls itself Jaish-al Muslimeen, or Army of Muslims, told AP it had no links to anyone detained in Kabul on Monday.

Akbar Agha also said in a telephone call the militants were "very close to an understanding" with government negotiators to exchange the hostages for 24 rebels in Afghan jails.

His claims could not be verified.

American officials worry a deal could encourage more abductions just as the military claims it is getting the better of Afghan insurgents using more conventional tactics.

U.S. troops killed one militant and captured three more in eastern Afghanistan on Monday after gunmen attacked their patrol, the military said. One American soldier was slightly wounded.