An Iraqi man with 18 pounds of explosives taped under his vest was arrested here Friday, thwarting what intelligence police today said was a plot to assassinate either President Hamid Karzai or the defense minister, Mohammed Fahim.

"He had been trained and assigned to carry out a suicide mission," Amrullah Salihi, spokesman for the National Directorate of Security, told journalists. "He had very clear links with the Taliban and some extremist Pakistani groups."

It was impossible to confirm the charges of an assassination plot, but both Afghan officials have been targets of previous attacks. In September, a gunman opened fire at Karzai's car in the city of Kandahar, and the same day a powerful car bomb exploded in Kabul. In April a convoy carrying Fahim in the city of Jalalabad was attacked by rockets.

Salihi would not say how police had learned about the man, whom he identified as a 22-year-old Iraqi Kurd named Bokan Akram Khorani. But he said the man had volunteered numerous details about himself and his alleged suicide mission after his arrest.

At a news conference in a hotel ballroom, police displayed several plastic packages of explosives wrapped in black tape and attached to wires, which they said were found on Khorani when he was arrested in an affluent Kabul neighborhood. They also showed photographs of a tall, bearded man they said was Khorani.

Salihi said the Iraqi man had been sent to assassinate Karzai on his return from a trip to the United States last week, but that he reached Kabul too late to ambush Karzai and switched to a plan to kill Fahim.

The intelligence police official said Khorani had been "casing" the neighborhood where Fahim lived when he was captured, and that police had been watching him since he arrived in the capital from Pakistan several days ago.

"He knew [Fahim's] movements in Kabul, which mosque he worshipped in and where he lived," Salihi said of the Iraqi man. He said the explosives found inside his clothing "could easily smash a car."

Salihi said Khorani had been trained in Pakistani Kashmir for the last four months before crossing the border into Afghanistan. He said Khorani had ties to three senior leaders of the former Taliban government who are now believed to be hiding in Pakistan, as well as to Pakistani extremist groups, which he did not name.

Pakistani Kashmir has long been a training base for terrorist groups fighting in India, Pakistan and Afghanistan. Afghan officials have recently warned that fugitive Taliban officials, possibly working with Pakistani intelligence agencies, may be joining forces with violent Islamic groups in Pakistan that are hostile to the Karzai government and its U.S. backers.

Khorani "bluntly admitted what his task was and said it would be an honor to succeed in the operation," Salihi said. He said the foiled plot, along with the arrest three months ago of an Uzbek man with a car full of explosives in Kabul, "clearly demonstrates . . . that the fight against terrorism is not over."

In the previous case, intelligence police also showed journalists explosives they said they seized from a car in Kabul, along with its foreign driver. They claimed he was a suicide bomber who planned to assassinate high-level Afghan officials. Salihi said that case is now "completed," but he did not elaborate.

It was unclear why a putative attacker would interchangeably target Karzai and Fahim, who are ethnic and political rivals with little in common. However, since they are the two most important officials in the Afghan government, the assassination of either man could destabilize the country.

Police did not say whether the Iraqi suspect was operating alone or with accomplices, but they said that at this point only he has been arrested.

They said he will be turned over to judicial authorities after their investigation is completed.

Amrullah Salihi, chief of the Afghan National Directorate of Security, holds a photo of a man arrested in Kabul with explosives and a detonator, which are displayed on the table.