Police say the attack happened on a bus.
Meanwhile, kidnappers in Iraq are reported to have extended by 48 hours their deadline to execute four Christian peace campaigners unless Iraqi detainees are freed.
Britain's foreign secretary, Jack Straw, appealed on 8 December to the kidnappers to contact British officials in Iraq. Straw did not say if he would negotiate with the kidnappers, but said he would like to "hear what they have to say."
In a separate development, Japanese Prime Minister Junichiro Koizumi said on 8 December that his government has decided to keep its roughly 600 non-combat troops in Iraq for up to a year.