BAGHDAD - Suicide bombers killed at least 19 people in Iraq on Thursday in separate attacks in Baghdad and the northern city of Kirkuk, security officials said, underscoring the fragility of Iraq's security gains.

In the latest attack, a suicide bomber struck at a crowded market in the south Baghdad district of Doura, killing 12 people and wounding 25 others, police said, adding that three U.S. soldiers were also killed.

The U.S. military could not immediately confirm this.

A sheet covered one body in Doura, and empty bandage packets littered a shop floor streaked with blood. A nearby hospital was packed with victims of the blast, which included an elderly woman and young men, some crying in agony.

An eyewitness said a U.S. patrol and some Sunni Arab anti-insurgent militiamen were at the entrance to the market when a man walked into the crowd and blew himself up.

There was chaos after the blast. Some people ran, others fell to the floor in fright, the witness, a policeman who declined to be named, said.

Earlier on Thursday, a bomber dressed in a security forces uniform mingled with Sunni Arab anti-insurgent militiamen in Kirkuk as they made their way to an army building to be paid, before triggering a vest packed with explosives.

Cars nearby were damaged by the blast, their cracked windshields spattered with blood. Shoes littered the area.

SPIKE IN VIOLENCE

The blasts come hours after a car bomb killed 40 civilians and wounded 82 others in Baghdad's poor, mostly Shi'ite district of Shula late on Wednesday, police said.

Al Qaeda and other groups have frequently targeted Shi'ites in Iraq, whom they consider heretics, but have also hit mostly Sunni anti-insurgent militias backed by Iraq's government, who have been credited with helping to sharply cut violence in Iraq.

Iraqi officials have lauded security gains in Iraq in the last year, but a rash of bombings in April made it the deadliest month for civilians since November.

Hazim al-Nuaimi, an analyst at Baghdad University, said insurgents may be trying to exploit tensions between the Sunni militias and the Shi'ite-led government, whom the militias sometimes accuse of failing to look after them.

Originally backed by the U.S. military, the Iraqi government has agreed to take over responsibility for paying the Sunni militias, and incorporate 20 percent into its security forces.

But perceived foot-dragging on this by the government and arrests of some militia leaders have stoked tensions.

The recent spike in attacks has raised doubts about whether Iraq can avoid sliding back into greater violence as the Iraqi military prepares to take greater security responsibility and U.S. troops prepare for a full withdrawal by the end of 2011.

(Reporting by Abdul Rahman Dhaher in Baghdad and Mustafa Mahmoud in Kirkuk; Writing by Mohammed Abbas; editing by Myra MacDonald)

Iraq