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KABUL, June 30 (Xinhua) -- Two suicide explosions hit a line of Afghan police buses in the western part of Kabul on Thursday, leaving at least 37 people dead, sources said.

Afghan security force inspect the site of a suicide attack in Kabul, Afghanistan, June 30, 2016. Two suicide explosions hit Afghan police convey of five buses in the western part of Kabul on Thursday, leaving at least 30 people dead, sources said. (Xinhua/Rahmat Alizadah)

The attack, which occurred at around midday in Qala-e-Haidar Khan, an area on the western outskirts of Kabul, also injured nearly 60 others.

"Five green-colored police buses were running along Kabul-Kandahar road. One suicide car bomber struck one bus at the middle of the convoy, forcing the vehicles to stop," witness Mohammed Karim told Xinhua.

"The second bomber arrived and detonated his car bomb roughly 20 minutes later after arrival of rescue teams and people."

Further details about the incident were still forthcoming amid the absence of official statement.

Sediq Sediqqi, spokesman of the Interior Ministry, told local media that nearly 30 people were killed and 58 others wounded.

"More details will be released to media later on the day after an ongoing investigation," he said.

The buses were reportedly carrying about 500 cadets and newly-graduates from a police training center in neighboring Wardak province to central Kabul.

The victims were travelling to join their families to celebrate the upcoming Eid festival which marks the end of Ramadan or fasting month.

Several bystanders were among the killed and injured, witnesses said.

One bus was destroyed and four buses and several civilian vehicles were damaged in the deadly attack.

Afghan President Mohammad Ashraf Ghani strongly condemned the incident.

Ghani has ordered a thorough investigation to find how decision on transportation of a large number of police graduates was made, according to a statement issued by the Presidential Palace.

The responsible officials must be held accountable if any dereliction found in the incident, the statement said.

Taliban militant group has claimed responsibility for the attack.

The Taliban-led insurgency has been rampant since early April when the militant group launched its annual rebel offensive in different areas of the country.

The Taliban urged civilians to stay away from official gatherings, military convoys and centers regarded as the legitimate targets by militants besides warning people not to support the government.

On June 10, a Taliban suicide attacker killed 14 people, including 12 Nepalese security guards, and injured nine others in eastern Kabul.