A shoe of one of the victims, is seen, on the ground as Iraqi forces stand guard the area after a car bomb explosion in the predominantly Shiite Bayaa district, southwestern Baghdad, iraq, on Sunday, Oct. 12, 2008. The bomb exploded Sunday in a commercial street of Baghdad killing seven people and wounding nine others, police said. (AP Photo/Hadi Mizban)

BAGHDAD (AP) — Suicide car bombers struck twice Sunday in the northern city of Mosul, killing at least six people and wounding dozens of others, U.S. and Iraqi officials said. A car bomb killed seven other people in Baghdad.

Two Iraqi soldiers were killed by snipers in separate attacks Sunday in the capital’s Yarmouk district, police said.

Also Sunday, the government announced new security measures to protect Christians in Mosul after a spate of attacks against them by Sunni religious extremists.

The series of attacks shows the ongoing security challenges facing Iraq as the U.S. shifts responsibility to this country’s own soldiers and police following the sharp decline in violence since last year.

The first attack in Mosul occurred when a suicide car bomber attacked a U.S. patrol, the U.S. military said. There were no American casualties, but five Iraqis were killed, including three young boys, the U.S. said. The attack also killed the bomber.