U.S. forces turned over a treacherous slice of southern Baghdad to the Iraqi army on Monday, one more step in a stuttering transition that U.S. leaders say needs to move faster.

The Iraqi troops took charge after months of training and running joint missions with American forces. U.S. officers say they're up to the task and the battalion's 32-year-old commander issued a defiant challenge to the insurgents whose murderous attacks helped the area earn its nickname, "Triangle of Death."

"The terrorists want to kill the Iraqi people," Col. Ali Fadil said following Monday's handover ceremony at a sprawling base on Baghdad's southern edge.

"But we will not allow this even if we have to sacrifice our own lives," Fadil said.

The handover is part of a process that could determine when U.S. forces can finally begin withdrawing, more three years after embarking on an occupation now facing a stubborn insurgency and growing killings among Shiites and Sunnis. President George W. Bush says he wants an Iraq that can "sustain and defend itself," but that's unlikely to happen until Iraqi forces can assume full responsibility for security.

U.S. officials say they're moving patiently, but have pressed Iraqi Prime Minister Nouri al-Maliki to set a timeline for achieving key security goals. Empowered by last week's U.S. elections result, opposition U.S. Democrats have been more forceful, saying al-Maliki has to realize the U.S. commitment isn't open-ended.

Fadil's troops of the 6th Iraqi Division, 4th Brigade, 5th Battalion — who are almost equally divided between Sunnis and Shiites — marched in tight formation at Monday's ceremony as an army band played selections including the British Army's "March of the Grenadier Guards."

Released from the formal parade, they shouted and sang, dancing with their AK-47s hoisted high in an age-old martial ritual.

Such scenes have played out at earlier transitions before, but with violence raging around Iraq, not all have ended smoothly.

At least twice last month, U.S. troops had to move back in to areas already turned over to back up Iraqi units overwhelmed by intense Sunni-Shiite fighting.

The challenge for Fadil's troops is especially serious because the area they cover is one of the toughest in Iraq, a 23-square-mile chunk of land that includes Dora, a neighborhood dominated by hardline Sunni supporters of former leader Saddam Hussein, and parts of the so-called Triangle of Death, a volatile Sunni district spreading southward toward the dominantly Shiite south.

Yet Fadil and his unit won high praise from the local U.S. commander, who called them the most proficient of any Iraqi unit now taking charge.

"He is a fierce warrior, he is a patriot, his loyalty is to the country of Iraq," said Col. Michael Garrett, commander of the 25th infantry Division's 4th Brigade. Garrett's forces will stay ready to help if needed and have posted combat advisers among the Fadil's units.

Another U.S. commander who has run missions alongside Fadil's troops said there was only a "negligible" gap with U.S. forces in discipline and ability.

Yet Lt. Col. Mark Odom hesitated when asked whether that can be reproduced on a national scale.

"I've just got sort of one frame in the film," Odom said. "Beyond that, I really can't tell you what the next frames will be."