BAGHDAD (Reuters) - Twin blasts in Baghdad on Friday, one exploding beside a pulpit during prayers, killed at least three people and wounded six, a Reuters witness and police sources said.

The attacks are the latest in a wave of violence that underline Iraq's struggle to overcome a stubborn insurgency eight months after U.S. troops left.

The first bomb detonated beside the pulpit, while a preacher was leading prayers at an outdoor mosque in the mainly-Shi'ite Sadr City neighborhood. Moments later, a second device, that had been hidden under weeds amid the worshippers, exploded.

"When the explosions happened, the worshippers stood up, but (the preacher) talked to us, asking us to stay in our places and keep quiet," Abu Ahmed, a 34-year-old worshipper, told Reuters at the scene.

Iraq's local al Qaeda wing has claimed attacks on Shi'ite neighborhoods and security forces as a revival of its campaign to provoke the Sunni-versus-Shi'ite sectarian violence that drove the country close to civil war four years ago.

Heightened tension between Shi'ites, Sunnis and Kurds in the coalition government since U.S. troops withdrew has raised fears of a return to sectarian violence of the kind that pushed Iraq to the brink of civil war a few years ago.

(Reporting by Kareem Raheem; Writing by Barry Malone; Editing by Alison Williams)