U.S. & World

BAGHDAD (CBS News) ― Iraqi forces engaged in heavy fighting with Shiite militias in the southern oil port of Basra Tuesday as a security plan to clamp down on violence between rival militia factions in the region began.

Col. Karim al-Zaidi, spokesman for the Iraq military, said security forces concentrated heavily in the city's center encountered stiff resistance from gunmen of the Mahdi Army, led by radical Shiite Cleric Muqtada al-Sadr.

AP Television News video showed smoke from explosions rising over the city and Iraqi soldiers exchanging gunfire with militia members.

Maj. Abbas Youssef, a police officer in the Basra hospital, said four civilians had been killed and at least 18 injured in the fighting.

CBS News chief foreign correspondent Lara Logan reports that as many as 10,000 Iraqi forces were involved in the operation, which was playing out in one of the country's most vital corners - extremely rich and on the border with Iran.

The violence threatens a months-long ceasefire declared by al-Sadr which is largely credited with easing the sectarian in the violence in many parts of Iraq.

Al-Sadr followers called for a nationwide civil disobedience campaign to protest raids and detentions later on Tuesday.

The head of the Sadrist parliamentary bloc says the move comes because of the continued U.S. and Iraqi actions against the Mahdi Army militia despite a cease-fire. Nassar al Rubaie has demanded that the raids stop, Sadrist detainees be released and an official apology be issued.

Logan says Iraqi officials maintain the operation in Basra is aimed at all militias operating in the city, but al-Sadr's Mahdi Army was clearly in the crosshairs, feeling the brunt of the attack, and defending themselves fiercely.

Witnesses who spoke to CBS News from Basra described hearing multiple explosions, and one man said bullets were flying through the windows of his house.

The clashes broke out after Iraqi authorities set an indefinite nighttime curfew on the city starting Monday. Iraqi Prime Minister Nouri al-Maliki also traveled to the volatile area to announce a new crackdown aimed at quelling rising tensions between rival Shiite factions vying for power.

The U.S. military said on Tuesday that five suspected militants were killed in Basra while attempting to place a roadside bomb. Ten others were injured after being spotted conducting suspicious activity, the statement said.

Security in Basra, about 340 miles southeast of Baghdad, had been steadily declining well before the British handed over responsibility for security to the Iraqis on Dec. 16. The British maintain forces in the area but did not immediately respond to a request for comment.

A British military spokesman told the British Broadcasting Corp. Tuesday that no U.K. forces were taking part in the operation in central Basra.

Al-Sadr's organization has threatened that tensions will escalate in Basra if members of al-Sadr's Shiite Mahdi Army are targeted.

"We are calling for calm, but this new security plan has the wrong timing," Harith al-Edhari, the director of al-Sadr's office in Basra, said Tuesday. "This plan is a government scheme to target the Sadrists as they did in Diwaniyah and Muthanna."

Al-Sadr's followers also have accused the Shiite-dominated government of exploiting a cease-fire to target the cleric's supporters in advance of provincial elections expected this fall. They have demanded the release of supporters rounded up in recent weeks.

The cleric recently told his followers that although the truce remains in effect, they were free to defend themselves against attacks.

There were reports Tuesday that al-Sadr, seen at left, might address followers in the Shiite holy city of Najaf in northern Iraq later in the day to discuss the clashes in Basra. The reports could not be immediately confirmed.

U.S. officials have insisted they are not going after Sadrists who respect the cease-fire but are targeting renegade elements, known as special groups, that the Americans believe have ties to Iran.

On Monday, al-Maliki relieved the top two security officials in Basra, officials said, and spent most of the day meeting with security officials around the city to determine what other security changes were needed.

At least one Iraqi battalion has already been sent to Basra, an official in the defense ministry said, speaking on condition of anonymity because he wasn't supposed to talk to the media. Other battalions may be called from Iraq's southern provinces.

The clashes follow recent fighting elsewhere in the country between U.S. and Iraqi forces and factions of the Mahdi Army. The Mahdi Army has come under severe strains in recent weeks as the U.S. and Iraqi forces detained followers they accuse of belonging to breakaway groups.

The U.S. military has accused Iran of arming and funding Shiite extremists to fight American forces in Iraq. Iran denies the allegation.

In other developments:

• Senior administration and military officials tell The New York Times that U.S. troop levels in Iraq will stay at similar levels during the previous five years of the war through 2008, according to plans presented To President Bush by Gen. David Petraeus, the top U.S. commander in Iraq, and the U.S. Ambassador to Iraq, Ryan Crocker.
  
  
• The FBI said it has recovered the remains of two kidnapped U.S. contractors in Iraq. The agency identified the contractors as Ronald Withrow of Roaring Springs, Texas, and John Roy Young of Kansas City, Missouri. Withrow worked for JPI Worldwide when he was kidnapped near Basra in January 2007. Young worked for Crescent Security Group when he was kidnapped in November 2006 in a separate incident. The FBI said the investigation into the kidnappings is ongoing.
  
  
• The White House said Monday it was "a sober moment" as the U.S. death toll in Iraq climbed to 4,000. President George W. Bush received a lengthy update on the war and aides said he was likely to embrace recommendations for a pause in troop withdrawals beyond those already scheduled.
  
  
• The U.S. military has said a series of rockets that fell on the highly-secured Green Zone in Baghdad on Sunday were Iranian-made and supplied by the Quds Force, an elite unit of Iran's Revolutionary Guards. The U.S. military has accused Iran of arming and funding Shiite extremists to fight American forces in Iraq. Iran denies the allegation. U.S. Embassy spokesman Philip Reeker said two government employees - an American and a Jordanian - were seriously wounded and six other people required medical attention after Sunday's volley of rocket attacks.

(© 2009 CBS Broadcasting Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)