A twin suicide bombing attack killed 23 people Wednesday in a car park crammed with vehicles supplying a major NATO base in Afghanistan's southern province of Kandahar, police said.

A suicide bomber on a motorcycle struck first and as a crowd gathered to help the victims a second bomber walked into their midst and set off explosives strapped to his body, provincial police chief General Abdul Raziq told AFP.

The attack happened in a parking lot holding dozens of trucks supplying the NATO-run Kandahar Air Base and a makeshift bazaar.Twenty-three people, all civilians, were killed and 50 others wounded, Raziq said, describing most of the victims as drivers, their assistants and workers.

"All casualties are civilians -- not a single military person," he said. Ahmad Jawed Faisal, a spokesman for the provincial administration, gave a similar account but said 22 people were killed.

The Kandahar Air Base is the largest NATO military base in southern Afghanistan, which has been a flashpoint for Taliban insurgents over the past decade.

There was no immediate claim of responsibility for the bombings, but similar attacks have been blamed on the hardline Islamists trying to topple the Western-backed government of President Hamid Karzai. The Taliban have in the past threatened to kill truckers working for the US-led NATO mission, which relies on civilian vehicles to supply their bases across Afghanistan.

The lorries go through complex security checks that can take days, so that dozens of trucks often mass outside military bases before being allowed inside to offload their cargo. Suicide attacks are a common Taliban tactic, along with roadside bombings that often miss their military targets and kill civilians.

For the past five years the number of civilians killed in the war has risen steadily, reaching a record of 3,021 in 2011.But the United Nations said last week that the civilian death toll in the first four months of this year dropped by 21 percent over the same period in 2011.

A total of 579 civilians died and 1,219 were wounded from January to April 2012, with Taliban-led insurgents responsible for the vast majority of the deaths, the UN said.

Kandahar is the birthplace of the Taliban, who took power in Kabul in 1996 and ruled for five years before being ousted in a US-led invasion for refusing to hand over al-Qaeda leader Osama bin Laden after the 9/11 attacks.