Insurgents have attacked a car in northern Iraq, killing three people who are reported to be foreigners. The driver also died.Witnesses say one of the victims was beheaded by the gunmen after he tried to escape. The incident happened in the northern city of Mosul, which has seen an upsurge in violence since last month when militants overran police stations and looted weapons. More than 150 bodies have been left on the city’s streets since early November. Some believe the killings could be linked to ethnic tensions between Kurds and Arabs.