A failed suicide bomber had taken delivery of his explosives-loaded Toyota near the Pakistan border, then headed into Kabul bent on blowing up President Hamid Karzai or some foreign "infidels," an Afghan intelligence chief said Wednesday.

"He has admitted he worked for Al Qaeda," Amrullah Saleh said of the suspect.

The plot fell apart when the car collided with another vehicle in the heart of the capital Monday morning and sped off, only to be cornered by pursuing police at a checkpoint.

The suspect is not Afghan, but his nationality and identity have not been established, said Saleh, national intelligence service director for Kabul.

The Afghan official told The Associated Press the "very sophisticated" car bomb, almost a half ton of explosives, was put together outside Afghanistan, implying the alleged plot originated in Pakistan.

Many Al Qaeda figures are believed to have taken refuge in Pakistan since a U.S.-led campaign toppled the Taliban regime last December and scattered the Afghan-based al-Qaida terror organization.

Saleh said the suspect told interrogators the names of those who "motivated" him. But the intelligence chief would not discuss what leads Afghan or other agencies might be investigating as a result.

Nor would he confirm what the Afghan Interior Ministry reported -- that an alleged Afghan accomplice, also unidentified, was arrested in the car with the suspected bomber. Saleh said the intelligence service held only one person, "the foreigner."

The alleged car-bomb plot was the latest development -- including the assassination last month of Vice President Abdul Qadir -- that has put the Afghan capital on edge. This attack was especially chilling because the shrapnel-packed Toyota Corolla had penetrated to a spot just hundreds of yards from the U.S. Embassy, Karzai's offices and the headquarters of the international security force patrolling Kabul.

"He has admitted his first target -- he was tasked to kill His Excellency Mr. Karzai," Saleh said. Failing that, he said, the bomber was to target government ministers or foreign compounds or facilities.

"He says he wanted to go to heaven by killing himself and also killing infidels and supporters of infidels in Afghanistan," Saleh said.

The suspect speaks Afghanistan's two major languages in a "broken" manner, Saleh said, and has a knowledge of Arabic and Russian.

Photographs of the car bomb showed yellow bricks of what was said to be C-4 explosives, tubes said to carry a liquid explosive, heavy batteries and connections, and two detonating buttons attached to the console near the gearshift.

It took experienced hands to fashion the bomb-on-wheels, Saleh said. "They put a lot of thought into it."

The bomb-rigged car originally was driven to the southeastern Afghan town of Khost and turned over to the foreign suspect, he said. Khost is 20 miles from the Pakistani border.

On Kabul's Microrayon Road, around the corner from the U.S. Embassy, the automobile collided with a sport utility vehicle, Afghan authorities said. When the Toyota sped from the scene, suspicious security officers gave chase.

During the pursuit, one of two Afghans in the car, clearly familiar with the neighborhood, jumped out and escaped, said the chief of Interior Ministry police, Gen. Din Mohammed Jurat.

The car was rushed by officers when it had to stop at a checkpoint about a half-mile from the accident scene. The car doors were found to be unusually heavy and were stripped, exposing bricks of C-4 explosives.

Maj. Angela Herbert, a spokeswoman for the International Security Assistance Force (ISAF) that patrols Kabul, said "valuable information" that ISAF shared a week ago with the Afghans may have contributed to foiling the plot.

Afghan intelligence officials said the information led them to deploy checkpoints and extra patrols in the city. But neither the Afghans nor the ISAF spokeswoman would elaborate.

Two car bombings in Karachi, Pakistan, in May and June killed 11 French engineers outside a hotel and 12 Pakistanis outside the U.S. Consulate. Pakistani authorities have blamed those attacks on Pakistani Islamic militants they say have ties to Al Qaeda.