Up to 20 percent of suicide car bombers in Iraq are from Algeria, a sign of growing cooperation between Islamic extremists in northern Africa and like-minded Iraqis, a senior U.S. military official said Tuesday.

The American officer said terror cells in the Middle East and northern Africa were increasingly joining forces as they face crackdowns in their own countries, leading to a stepped-up flow of money and Islamic extremists to Iraq.

Forensic investigations have revealed that 20 percent of suicide car bombers in Iraq are Algerian and roughly 5 percent come from Morocco and Tunisia, according to the officer with responsibilities in Europe and Africa. The officer spoke on condition of anonymity, preferring for reasons of protocol to let U.S. commanders in Iraq speak on the record.