Saudi security forces and police surrounded a house in the capital Wednesday, but withdrew from the area hours later, witnesses said. It was unclear whether anyone was detained.

Security officials would not comment on the operation, which blocked off the entire district of Al-Badeaa, in southwestern Riyadh (search), for at least three hours while security forces closed in on one house.

Witnesses said they heard gunfire and the anti-terrorism force use loudspeakers to urge those inside the house to surrender.

It was unclear whether anyone was in the house at the time. The witnesses said security forces later searched the house and a nearby mosque before the large force withdrew from the area.

The police cars and armored personnel carriers that blocked the roads then pulled out, leaving just a couple of police cars at the square marking the entrance to the neighborhood.

The operation came as Saudi Arabia stepped up its search for the kidnappers of Paul Johnson (search), an American taken hostage Saturday by a group calling itself Al Qaeda (search) in the Arabian Peninsula.

Witnesses who were diverted from the area by police speculated that the house may be the hideout of the suspected kidnappers. However, security officials would not comment on who may have been in the house.

On Tuesday, Saudi forces arrested two militants north of Riyadh as they increased security while hunting for Johnson's kidnappers.

An Islamic Web site screened a videotape of Johnson, 49, of Eagleswood Township, N.J., on Tuesday in which his captors threatened to kill him unless the Saudi government freed all its Al Qaeda detainees by Friday.