The U.S. embassy in Islamabad denies that any Americans were killed in a deadly blast Monday in northwest Pakistan.

Earlier, Pakistani officials said a suicide car bomber had killed two Americans in the explosion in the city of Peshawar, near Pakistan's semi-autonomous tribal region along the Afghan border. Some reports said two Pakistanis died.

There are conflicting reports on whether more than two people were killed in the attack, which authorities say left several people wounded.

Officials say the attacker rammed his explosive-laden vehicle into a U.S. government car. Police say the bomber's vehicle was loaded with 110 kilograms of explosives.

The explosion happened in an area of Peshawar that is home to several foreign aid organizations and the United Nations.

The bomber struck the vehicle after it left the U.S. consulate.

No one has claimed responsibility for the attack.

The Pakistani Taliban, the Afghan Taliban, al-Qaida and affiliated militant groups are entrenched in the tribal regions and take advantage of the porous border to launch attacks against NATO and Afghan forces in Afghanistan.