A suicide bomber blew himself up outside a court building in Peshawar on Thursday, killing 18 people, officials said.

"The attacker was on foot and blew himself up when guards tried to search him at the gates of the court," senior city administrator Sahibzada Anis told reporters.

Eighteen people were killed and 34 wounded in the attack at the court complex, said hospital official and doctor Sahib Gul.

Three policemen were among the dead, said Anis.

There was no immediate claim of responsibility for Thursday's bombing.

Pakistan launched 30,000 troops, backed by war planes and attack helicopter, into a three-pronged offensive against suspected bases of Tehreek-e-Taliban into South Waziristan on October 17, an operation that has been strongly endorsed by the United States.

The United Nations said Wednesday that 268,000 people have been verified as displaced by the offensive, staying with relatives, friends, host families or in rented houses, and the UN is helping distribute tents and other aid.

US drone attack

Earlier, security officials said a U.S. drone aircraft fired two missiles into a northwestern region, killing four people.

The late night attack was in the North Waziristan region on the Afghan border, about 20 km (12 miles) west of the town of Miranshah, the officials said.

The identity of the four people killed and six wounded was not known, said the officials, who declined to be identified.

The United States has carried out 44 attacks with its pilotless, missile-firing aircraft in northwest Pakistan this year as it occupies neighbouring Afghanistan.

There were 32 such strikes last year, according to a Reuters tally of reports from Pakistani security agents, government officials and residents.

Agencies