KABUL, June 6 (Xinhua) -- Afghan presidential front-runner Abdullah Abdullah escaped unhurt a twin blast on Friday in Kabul in an attack that killed four civilians and injured several others, sources said.
"Abdullah's convoy was running from Ariana Kabul Wedding Hall where Islamic Unity Party, leading by Mohammad Akbari, endorsed him. A suicide car bomb went off close to Abdullah vehicle near the hall. A roadside bomb followed the first blast," a security source told Xinhua at the scene.
He said four civilians were killed and several people were injured in the attack.
The attack took place as Afghanistan is preparing for the presidential runoff between Abdullah and his rival Dr. Ashraf Ghani Ahmadzi to be held on June 14.
According to the final results of the April 5 presidential election, Abdullah secured 45 percent of some 7 million votes, Ahmadzai won 31.6 percent.
The two front-runners entered runoff after none of the eight candidates obtained an outright victory or more than half of the valid votes in the first round.
Earlier on the day, Abdullah, a former foreign minister said his vehicle was destroyed in the attack. He said several of his bodyguards were wounded.
The election campaign started on May 22 and will end on June 11.
The runoff preliminary results will be clear on July 2 while the final result of the will be announced on July 22.
Nearly 7 million Afghans of some 12 million eligible voters cast their ballots amid Taliban threat of violence to elect a successor to the outgoing President Hamid Karzai who has ruled the war-torn country since the Taliban regime was toppled in late 2001.
The exact number of casualties remained unknown as the government did not release statement on the incident. The explosions had also damaged the hall building and several vehicles running on the street.
Local analysts said that insecurity was the biggest challenge for the upcoming polls. The Taliban insurgent group, which opposes the polls, had launched a rebel spring offensive on Monday.
Nearly two dozens of civilians and security forces were killed and about 100 others wounded in Taliban-led attacks in April 5 election.
Abdullah and Ashraf Ghani Ahmadzai, the former finance minister, strongly condemned the attack.