Afghanistan's spy chief will be evacuated abroad for specialist treatment after being wounded by a Taliban suicide bomber, the government said Monday as further details emerged of the brazen attack.

President Hamid Karzai told his national security team that Asadullah Khalid's condition was improving at a US-run military hospital near Kabul but that he will be flown abroad for better treatment.

A statement from the presidential palace did not specify which country Khalid would be sent to. As some of Khalid's family live in the United States it is seen as likely that he will be flown there, an official said.

Khalid was wounded Thursday by a man posing as a Taliban peace envoy, who detonated a bomb hidden in his underpants at a guest house run by the intelligence agency in Kabul.

A senior government official told AFP that Khalid, who suffered injuries to his abdomen, was unable to speak but none of his major organs were damaged.

"He's conscious, he recognises people but can't talk. He waved his hand when Karzai met him," the official, who spoke on condition of anonymity, told AFP.

Citing US military doctors, the official said the head of the National Directorate of Security (NDS) was expected to remain in hospital for up to three months.

Based on the witness account of a man who survived the attack, the official said the attacker was about a metre (3.3 feet) from the spy chief when he detonated the bomb.

"When Khalid arrived, the bomber was eating with another guy from the NDS," he said.

"Khalid arrived with another colleague named Massoud. At the beginning the attacker seemed like he was not sure which one was Khalid.

"At this stage, Khalid's phone rang. From his talking on the phone, the bomber appeared to recognise him, and approached him and detonated himself."

The president has ordered a committee investigating the attack to report back to him in two days.

Karzai told a press conference on Sunday that the bombing had been planned in neighbouring Pakistan, a charge rejected by Islamabad.