A bomb exploded in downtown Kabul, wounding at least 10 people, and five Afghan laborers were ambushed and fatally shot on their way to a U.S. military base in eastern Afghanistan, police and officials said Tuesday.

The bomb that went off in the Afghan capital had been planted in a hand cart behind a car, said police official Mohammed Nabi. The explosion took place at a busy traffic intersection near the presidential palace, shattering windows at a cinema and the nearby Justice Ministry.

Ten people were wounded by the blast, according to Health Ministry official Buz Mohammad Qadiri. Four had minor injuries and were treated and released. Six others remain hospitalized, he said.

"We don't know what was the target of this bomb," said Ali Shah Paktiawal, criminal director of Kabul police, adding that an investigation was under way.

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Mohammad Rasoul, 52, a driver whose taxi was damaged in the explosion, said he was inside his car when the blast occurred.

"It was a very heavy explosion, and it happened only five to seven meters (16-23 feet) from my car," he said. "The glass windows were blown in toward me. When I turned my head, I saw one man with both legs cut off and he was screaming."

The attacks come amid an upsurge of violence by Taliban-led rebels, particularly in the lawless south and east of the country. Bombings are less common in Kabul.

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Earlier Tuesday, a roadside bomb went off in the east of the city, near a bus bringing Interior Ministry officials to work, wounding one of them, said ministry spokesman Yousuf Stanezai.

The attack on laborers happened Monday in eastern Kunar province as they traveled in a truck delivering construction wood to a U.S. military base, said Abdul Jalal Jalal, the provincial police chief. A sixth laborer was wounded, while the driver of the truck managed to escape unhurt.

Jalal said he suspected that Taliban militants were responsible for the killings in the Karangal area and that the laborers had been targeted because they were working at the base.

Late Monday, a suicide attacker hit a checkpoint in southern Kandahar city, killing himself and a policeman and injuring six others. The blast sent body parts flying all over the pavement, according to an AP reporter on the scene.

The attacker walked up to the checkpoint on foot before blowing himself up, said police commander Agha Lala. Among the injured were three policemen and three bystanders.

Since May, more than 600 Afghans, mostly militants, have been reported killed in violence, according to an Associated Press tally based on U.S.-led coalition and Afghan figures.

The upsurge in rebel violence has prompted a tough response, with more than 10,000 Afghan and coalition troops deployed in a massive military campaign in the volatile south, billed as the largest since the Taliban regime was ousted in 2001.

Also, the U.S. military announced Monday it was giving US$2 billion (euro1.56 billion) worth of weapons and vehicles to modernize Afghanistan's national army to help fight the insurgents.

The equipment will include 2,500 Humvees, tens of thousands of M-16 assault rifles, flak jackets and construction of a national military command center.