Hundreds of Iraqis shouted and burned American flags in the streets of Baghdad to protest the visit of U.S. Vice President Joe Biden.

The followers of anti-American Shi'ite cleric Moqtada al-Sadr marched through the slum of Sadr City Friday just as the vice president called on leaders of Iraq's political factions to settle their differences.

US Vice President Joe Biden (File photo)

Biden is making the first trip to Iraq by a top U.S. official since U.S.-led troops pulled out of Iraqi cities and towns.

He said the troop withdrawals are only part of the process.  He said Iraqi leaders must tackle unresolved issues, including what to do with oil revenues and boundary disputes.

The vice president met Friday with the commander of U.S. forces in Iraq, General Ray Odierno, and is scheduled to talk with Prime Minister Nouri al-Maliki and President Jalal Talabani.

Iraq's defense ministry says it already is looking ahead to the next phase of the U.S. troop withdrawal, which will see the U.S. remove about 100,000 troops from the region.

Biden's visit comes as violence in Iraq reached its highest levels in about eight months.

Earlier this week, the U.S. withdrew combat troops from urban areas in Iraq.

About 130,000 U.S. troops remain in Iraq to conduct combat duties outside cities, and to advise Iraqi forces within cities.

President Barack Obama has urged Iraqi leaders to do more to resolve internal differences.  On Tuesday he appointed Biden to oversee Iraq policy.