Updated

U.S. military officials were guardedly optimistic Friday about the immediate success of a joint operation with Iraqi forces meant to break the back of sectarian violence that has pushed the nation to the brink of civil war.

Ten bodies were found on the streets of Baghdad today, apparent victims of sectarian violence and gang fighting. This is a sharp reduction from the daily body counts of 40 or more that have been common recently, said Brig. Gen. Qassim Moussawi, a spokesman for the joint U.S.-Iraqi security sweep that began this week.

The reduction in violence was due not only to increased security, but also to an apparent decision by militias and insurgents to lay low, said Maj. Gen. Joseph Fil, commander of U.S. forces in Baghdad.

"But make no mistake, we do not believe ... that's going to continue, and we do expect there are going to be some very rough, difficult days ahead," Fil said. "And this enemy knows how — they understand lethality and they have a thirst for blood like I have never seen anywhere before."

"I would say that it is way too early to establish any trends," said Lt. Col. Chris Garver, a U.S. military spokesman. "We've just started to focus our operations. We have months to go to see if we are going to succeed or not."

The contrasting outlooks cut across the entire mission, dubbed Operation Law and Order, which seeks to reclaim the streets. Powerful militias and freelance vigilantes have carved Baghdad into fiefdoms and made even daily errands a gamble that could end with a car bombing or gunfire.

The Iraqis are eager to show clear progress to boost the leadership of Prime Minister Nouri al-Maliki. U.S. commanders, however, are approaching the neighbor-by-neighbor sweep as a methodical campaign without quick victories — learning from past mistakes of pouring through an area, only to find that militiamen simply went underground and returned after American forces left.

"We are just at the beginning stages," reminded Garver.

But evidence of the offensive against militants appeared around the country.

Borders to Iran and Syria have been temporarily sealed in attempts to foil suspected supply routes. In Diyala province northeast of Baghdad, U.S. forces are under sharply escalating attacks from Sunni Muslim insurgents — suggesting that some groups have shifted from Baghdad to other areas to sidestep the crackdown in the capital.

U.S. military officials said demolition experts destroyed a bomb-making factory they linked to the al-Qaida in Iraq faction in Salman Pak, just southwest of Baghdad. The statement said the workshop contained about 1,000 pounds of explosives.

But doubt was cast on another reported blow to Al Qaeda in Iraq.

The Interior Ministry said that leader Abu Hamza al-Muhajir, also known as Abu Ayyub al-Masri, was wounded and an aide killed Thursday in a clash with Iraqi forces near Balad, north of Baghdad.

Garver, the U.S. military spokesman, later said the Pentagon had no information that al-Masri was hit. The al-Masri deputy reported killed, identified as Abu Abdullah al-Majemaai, was detained last week and remains in jail, said an Iraqi army officer, who spoke on condition of anonymity because he was not authorized to disclose the information.

In a statement posted on an Islamic militant Web site on Friday, the al-Qaida-affilated Islamic State of Iraq purportedly denied that al-Masri was wounded. It said the Iraqi government was "making up such news that has been denied even by their masters, the Americans."

Iraqi security officials also said 34 armed men belonging to a messianic Shiite cult were detained near Hillah, about 60 miles south of Baghdad.

The Soldiers of Heaven, or Jund al-Samaa, cult was involved in a fierce gun battle last month with Iraqi forces who accused it of planning to kill Shiite clerics and others in a bid to force the return of the "Hidden Imam" — a descendant of the Prophet Muhammad who disappeared as a child in the 9th century. Shiites believe he will return one day to bring justice.

In mosques Friday, some Muslim clerics supported the general goals of the military push to calm Baghdad. But others used the weekly prayers to denounce the American troop buildup in Baghdad.

Political leaders, too, quarreled over the widening security sweeps — reflecting starkly opposing perspectives among Iraq's two Muslim groups.

The majority Shiites have generally favored the campaign as a way to neutralize Sunni militant groups, blamed for waves of recent car bombings. Sunnis — who enjoyed a privileged position under Saddam Hussein — believe Shiite factions will use the military push to try to cement controls of key areas in Baghdad.

Sunni lawmaker Dhafir Al-Ani said on Al-Arabiya television that the Baghdad security plan had lost the "element of surprise" because it was announced long in advance, giving Shiite militiamen time to flee to Iran. He also claimed Shiite militias had provided security forces with some of the names on their wanted list.

But a Shiite lawmaker, Hadi Al-Amiri, backed the U.S.-Iraqi crackdown as a way to "target all those who cause the Iraqi bloodshed."

In Geneva, the International Organization for Migration offered a bleak picture of Iraqis trying to escape the violence and insecurity. Nearly 18,000 people have left their homes in the past three weeks in central and southern Iraq — some fleeing for the borders and others taking shelter in makeshift housing.

As many as 1 million Iraqis could flee their homes this year unless the unrest is brought under control, said a report by the 120-nation agency. An estimated 1.4 million Iraqis have already left their homes.

"The numbers of people that are being displaced are increasing every day," said Jemini Pandya, a spokeswoman for the group. "The security situation is not improving. It's not changing."

The Associated Press contributed to this report.