A suicide bomber has killed at least 11 people in Afghanistan's capital, Kabul, after targeting a police bus. Rising violence in Afghanistan, now at the highest level since the U.S.-led invasion in 2001, has prompted the offer of new rewards for the capture of Taleban commanders. Daniel Schearf reports from Islamabad.

The suicide bomber killed at least six police and five civilians, including three school children, after trying to board a police bus on Tuesday.

Afghanistan's Interior Ministry spokesman, Zemarai Bashari, said seven other people were injured in the blast. He said one policeman on the bus shot the bomber as he tried to get on board, but he was still able to detonate his explosives.

"The police that was sitting in the front seat did a very brave job and he was really a hero," said Bashari. "He stopped the bomber and warned him to stop. But, after not obeying the orders, he opened fire on the bomber and after getting injured the bomber blew himself up."

The attack was the second suicide bombing in Kabul since Saturday when a similar bomber targeted an Afghan Army bus, killing 30 people and injuring many.

A purported Taleban spokesman has claimed responsibility for both bombings.

Afghanistan has suffered a big jump in suicide bombings in recent years, from only a few in 2004 to more than 100 so far this year.

A United Nations report last month said most Afghan suicide bombers were trained or supported in neighboring Pakistan's tribal regions where Taleban militants are believed to have bases and are strongly supported by locals.

The report said many suicide bombers are recruited from Pakistani religious schools and are often coerced into sacrificing themselves.

Violence in Afghanistan has increased dramatically since the U.S.-led invasion drove the Taleban from government and into hiding. Several thousand people have been killed in the last year alone.

The U.S. military has issued new rewards, of up to $200,000 each, for information leading to the capture of twelve mid-level Taleban commanders.

The Afghan president has also offered to hold peace talks with the Taleban. The militant Islamic group refuses to enter into any talks as long as foreign troops remain in Afghanistan.