KARACHI, Pakistan — A suicide attacker rammed a car packed with explosives into a vehicle carrying an American diplomat in Pakistan's largest city, killing four people — including the diplomat — ahead of President Bush's visit to Pakistan.

Bush condemned the attack near the U.S. Consulate and a luxury hotel in Karachi, and said "terrorists and killers" would not prevent him from going to Pakistan on the final leg of his tour of South Asia.

"We have lost at least one U.S. citizen in the bombing, a foreign service officer, and I send our country's deepest condolences to that person's loved ones and family," Bush said at a news conference in neighboring India, without naming the diplomat.

The blast ripped through the parking lot of the Marriott Hotel, about 20 yards from the consulate gate, shattering windows at the consulate and on all 10 floors of the hotel. Ten cars were destroyed, and charred wreckage was flung as far as 200 yards.

Initial investigations showed a suicide attacker deliberately rammed his car into a vehicle carrying the U.S. diplomat, blowing it into the air, across a concrete barrier and into the grounds of the hotel, a Pakistani counterterrorism official and senior investigator said on condition of anonymity because they were not authorized to speak to the media.

The driver of the diplomat's car, a Pakistani working for the consulate, also died. The other fatalities were a paramilitary guard and an unidentified woman.

The attacker was also presumed killed in the attack, the two security officials said. His body was not recovered.

The counterterrorism official said the attacker used high-intensity explosives and it was the most powerful blast he'd seen in Karachi — a hotbed of Islamic militancy.