Nearly 4,000 American soldiers poured into Baghdad this week, the fourth of five brigades being sent to strengthen an 11-week-old crackdown aimed at quelling sectarian violence, the U.S. military said Wednesday.

But while the U.S. and Iraqi militaries moved to complete an increase of forces in the capital, bombings, shootings and mortar attacks left at least 47 people dead across the country.

The developments came on the eve of an international conference in the Egyptian resort of Sharm el-Sheik in a bid to boost world economic and diplomatic support for Iraq and reduce the tide of sectarian violence and terrorism there.

U.S. Secretary of State Condoleezza Rice acknowledged international resistance to new financial and political support for Iraq — particularly debt relief.

"The region has everything at stake here; Iraq's neighbors have everything at stake here," Rice told reporters traveling with her to a gathering that will include U.S. adversaries Iran and Syria.

Rice said the history of troubled relations between Iraq and its neighbors predates the U.S.-led invasion of 2003, but said Middle East states should understand the risk they face from a failed Iraq.

"Iraq is at the center of either a stable Middle East or an unstable Middle East, and we should therefore all align our policies in ways that contribute to stability," Rice said.

The U.S. military said Wednesday that the fourth of five brigades being sent to help Iraqi security forces as part of the crackdown had arrived this week.

The 4th Brigade, 2nd Stryker Brigade Combat Team from Fort Lewis, Wash., which includes about 3,700 soldiers, will be deployed in the Baghdad area and in northern Iraq, the military said. Officials want the rest in place by June, for a total in Iraq of 160,000.

U.S. military spokesman Rear Adm. Mark Fox said Wednesday that Iraqi and U.S. forces now have 57 joint security stations and combat outposts in the Baghdad area and that "while the security situation remains exceedingly challenging, we've seen some encouraging signs of progress."

"We continue to see a reduced total number of sectarian incidents in comparison to before the Baghdad security operation, including murders and kidnappings," Fox told reporters in Baghdad. But he said car bomb attacks have increased, including some with very high casualties.

When complete, the Baghdad security operation will include about 28,000 additional U.S. forces, including 20,500 combat soldiers and about 8,000 service members involved in support services such as intelligence, military police and logistics.

Brig. Gen. Qassim al-Moussawi, an Iraqi military spokesman, said most of the crackdown's operations were taking place in volatile areas outside Baghdad, including the Sunni cities of Mahmoudiyah and Madain.

Al-Moussawi said insurgent operations had dropped significantly in Baghdad as the groups had fled to other areas.

"Next week will witness more military operations in both halves of Baghdad," he said, referring to the two sides of the Tigris River that divides Baghdad. "Almost all our military operations are now taking place on Baghdad's outskirts."

But sectarian attacks persisted, with at least 47 violent deaths reported by police.

The deadliest occurred at dusk, when a suicide car bomber detonated his payload near a police station and a bus station in Baghdad's largest Shiite district Sadr City, killing at least nine people — three policemen and six civilians — and wounding 34, police said.

The explosion also damaged several shops selling ice cream and fast food in the area, along with a few civilian vehicles and city buses, witnesses said.

Ahmed Mohammed Ali, 31, who owns a kiosk selling ice cream and cigarettes, said he was wounded in the chest after a big explosion, followed by a huge fire that sent black smoke billowing into the air.

"I saw police and civilian cars on fire," he said. "There were several wounded people, including women and children and most of the wounds were caused by burns. There were charred bodies near pools of blood. I helped carry the wounded to a nearby hospital despite my injuries."

Gunmen killed the three Sunni brothers about 3 a.m. and set the house on fire in a religiously mixed neighborhood of Risala in western Baghdad, police said.

A bomb exploded near a house belonging to a displaced Shiite family in Hillah, about 60 miles south of Baghdad, killing a man and wounding his wife, according to provincial police.

Elsewhere, a roadside bomb struck a minibus in Mahmoudiya, 20 miles south of the capital, killing eight people and wounding one, police said. The bus was carrying passengers to Baghdad. Two mortar rounds also fell on a residential area in the volatile city, killing three people and wounding 13, police said.

At 3:45 p.m., two mortar shells hit a house in the Shiite Shaab neighborhood of northeastern Baghdad, killing three residents and wounding nine, police said.

Gunmen also killed a university professor in the northern Iraqi city of Mosul as he was driving home from work

At least 19 bullet-riddled bodies — apparent victims of so-called sectarian death squads — also were found, including 10 in the northeastern city of Baqouba.

The security efforts come as U.S. President George W. Bush is engaged in a fierce debate with the Democratic-led Congress over the war. Bush vetoed legislation to pull U.S. troops out of Iraq in a historic showdown with Congress over whether the unpopular and costly war should end or escalate.

The measure would require the first U.S. combat troops to be withdrawn by Oct. 1 with a goal of a complete pullout six months later.

Democrats accused Bush of ignoring Americans' desire to stop the war, which has claimed the lives of more than 3,350 members of the military.

Ismail Qassim, a 41-year-old Shiite electricity ministry employee in Baghdad, welcomed the veto.

"In spite of all the problems Iraq is facing because of the American presence, there is some need for them at least for one more year because of the sectarian strife in Iraq and corruption in the security services," he said.

Sameer Hussein, a 22-year-old Sunni college student in Baghdad, said he wanted the U.S. forces to withdraw but didn't think they ever would.

"Even if they will withdraw they will leave permanent military bases in Iraq and that is something Iraqi people will reject," he said.