A suicide bomber has killed at least 10 people and wounded more than 20 others inside a Shi'ite mosque in Baghdad.  The deadly explosion came as a massive security operation continued in the Iraqi capital.  Despite the violence, a top U.S. military official says the level of bloodshed in Baghdad has dropped in recent days.

Iraqi police say the bomber walked into the Buratha Mosque as worshipers began to gather for Friday prayers.

Witnesses on the scene say the man hid the explosives in his shoes, and blew himself up when confronted by guards.

The mosque, which is used by members of Iraq's Shi'ite majority, has been attacked before. In April, three suicide bombers targeted worshippers, killing more than 70 people.

The violence came during a massive security operation in Baghdad, ordered by Iraqi Prime Minister Nouri al-Maliki in an effort to curb sectarian violence and attacks by al-Qaida insurgents.

Speaking to reporters at the Pentagon via teleconference from Baghdad, U.S. Major General James Thurman said the operation is designed to disrupt terrorist cells, and target groups opposed to the Iraqi government.

"We have seen a drop in violence, and expect that trend to continue with the implementation of the Baghdad security plan," he said.  "We will put more Iraqi security forces in the lead in the coming days."

Tens-of-thousands of Iraqi troops and police, backed by coalition forces, are patrolling in Baghdad.

General Thurman says, it is important to note that Iraqi forces are leading the effort.

"This security of Baghdad is about Iraqis," he added.  "This is about Iraq, the Iraqi government, stepping forward, and taking action to lower this violence.  That is what this is about.  This is not about the coalition, and I want to stress that point."

The crackdown, which began earlier this week, and is dubbed Operation Forward Together, is one of the largest since the U.S.-led invasion in 2003.

The effort follows the death of the leader of al-Qaida in Iraq, Abu Musab al-Zarqawi, in an air strike last week.