Suicide bombers have tried to kill Afghanistan's Senate leader, in an attack in which four people died.
There have been 12 suicide attacks already in Afghanistan this year
Sibghatullah Mujaddedi, who also leads a government commission seeking reconciliation with the Taleban, escaped unhurt in the blast.
But two civilians were killed as well as the two attackers, when their vehicle carrying explosives blew up near his convoy in the capital Kabul.
Mr Mujaddedi blamed Pakistan's spy agency, but Pakistan denied the claim.
He told reporters after the attack he had "information" that the ISI planned to kill him because of his efforts to engage the Taleban in the peace process.
"In the past months I have got [information] from six sources that the ISI had sent people to Afghanistan to assassinate me."
Mr Mujaddedi said the "ISI had inflicted more damage on Afghanistan than the Russians".
'Jealous of peace'
Pakistani foreign ministry spokesperson Tasnim Aslam told the Associated Press news agency the charge was "baseless".
Afghan President Hamid Karzai, who got in touch with Mr Mujaddedi immediately after the incident, has condemned the attack.
"The attack shows enemies of Afghanistan are jealous of its peace and stability," he said.
Mr Karzai said his government had information for the past two months of "plans being made" to assassinate some political personalities, including himself and Mr Mujaddedi.
He did not, however, mention who were making these plans.
Mr Mujaddedi was driving to work when the attackers struck on a busy street near one of Kabul's two universities, police said.
A pick-up truck approached Mr Mujaddedi's car and exploded, Baz Noor, one of the former president's bodyguards, was quoted as saying by the AFP news agency.
"Our car was damaged but no-one was hurt," Mr Noor said.
The powerful blast shattered windows in houses more than a kilometre away.
Mr Mujaddedi was the first president when Mujahideen fighters seized power from the Soviet-backed regime in 1992.
He has urged all Taleban fighters to lay down their guns and criticised neighbouring Pakistan for supporting the movement, the BBC's Mike Donkin in Kabul says.
The former president has also played a key role in bringing former Taleban leaders into the reconciliation process, our correspondent says.
Mr Mujaddedi is a close political ally of President Hamid Karzai, who has condemned the attack.
Afghanistan has seen a recent string of suicide attacks, most of them in the south of the country.
There have been 12 suicide attacks already in Afghanistan this year compared with 17 attacks last year and just five attacks in 2004.
Last year, attacks mainly in the south and east left more than 1,400 people dead.
It was the country's bloodiest year since US-led forces ousted the Taleban in late 2001.