Gunmen fired on supporters of radical Shiite cleric Muqtada al-Sadr (search) Friday, killing one person and injuring two others as they made their way to protests planned for the second anniversary of Baghdad's fall to U.S.-led troops.

In the poor New Baghdad (search) neighborhood, four children were also killed Friday when they came across an explosive device while digging through garbage for metal scraps, witnesses and police said. It was unclear what caused the blast.

"It's really ironic," said Qais Mousa, who saw the fatal explosion. "We are living in a rich country, while these poor innocents are dying in this horrible way."

The capital braced for massive protests Saturday, two years to the day since the fall of Baghdad. Shiite and Sunni religious asked their supporters to hold demonstrations to demand that U.S.-led troops leave.

Al-Sadr, who led uprisings against the U.S.-led coalition last year, called on his supporters to stage a mass protest at Firdos Square (search), where jubilant demonstrators pulled down a statue of Saddam Hussein two years earlier, marking the beginning of a U.S.-led occupation of the country.

Sheik Hassan al-Edhari (search), an official at al-Sadr's Baghdad office, said the protesters will demand that the new Iraqi government set a schedule for pulling out foreign troops and for trying Saddam.

Later Friday, gunmen opened fire on a group of al-Sadr's supporters who had recently arrived from the Shiite city of Karbala to participate in Saturday's protest, killing an official at al-Sadr's office in Karbala, Fadhil al-Shawky.

During his Friday morning sermon in the capital, the head of the Association of Muslim Scholars in Iraq, an influential Sunni group, also called for all Iraqis to protest the U.S. occupation and accused U.S.-led coalition forces of "killing the Iraqi people daily."

"We demand that the occupation troops withdraw from Iraq. We don't want them to do it immediately, but we want them to set a timetable for their withdrawal," said Sheik Harith al-Dahri, whose group is believed to have ties to insurgents.

But in another sermon at a major Sunni mosque in Baghdad, Sheik Ahmad Hasan al-Taha instructed worshippers to refrain from marking the April 9 anniversary. Al-Taha also called for the release of arrested religious figures, claiming there were more than 90 imams in detention.

The U.S. military said they had nothing planned to mark the anniversary, and officials refused to comment on security measures. But additional Bradley Fighting Vehicles and humvees were seen in areas where the protests were expected.

Iraq's new interim government has reached out to the country's Sunni minority, naming Sunni Arab leaders to top posts. But Sunni religious and political leaders have continued to distance themselves from the interim government.

Sunnis, once-dominant under Saddam Hussein, are believed to make up the backbone of the insurgency.

Sunni Arabs only have 17 seats in parliament, largely because many boycotted the Jan. 30 elections or stayed home for fear of attacks at the polls. Shiites have 140 of the 275 seats in the National Assembly, while Kurds have the second largest bloc with 75 seats.

Violence continued in the rest of the country Friday.

Three masked gunmen killed an Iraqi Army officer, Maj. Mahmoud Hassan al-Yassiri, late Thursday in the southern city of Basra, Capt. Firas al-Timimi of the Iraqi Army said.

In the Shiite holy city of Najaf, four civilians were injured by a bomb that exploded near a bus station, local police Capt. Qussai al-Jazaeri said.

A U.S. Marine was killed Wednesday in a vehicle accident during combat operations in Fallujah, the military said Friday in a statement.

Jordan, which has had sometimes strained relations with the outgoing government due to accusations that it wasn't taking full measures to stop insurgents from crossing into Iraq, sent a telegram congratulating Iraq's new leaders.

Jordan's King Abdullah II said his country would help Iraq "overcome this current period and achieve its aspirations in the rebuilding process," the official Petra news agency reported late Thursday.