Baghdad, Iraq ? The leader of Iraq’s largest Shiite political organization joined the country’s most revered and powerful Shiite cleric Saturday in a strong public push for voter support of a new constitution, three weeks ahead of a national referendum.

Also, suicide car bombers killed five Iraqis in and near the capital, and the U.S. military said a soldier died in a roadside bombing Friday night in southeast Baghdad. The death raised to 1,913 the number of U.S. service members who have died in Iraq since the war started in March 2003, according to an Associated Press count.

In Basra, the country’s southern oil hub and headquarters for Britain’s 8,500-strong force, an Iraqi judge said he renewed homicide arrest warrants for two undercover British soldiers who allegedly killed an Iraqi policeman trying to detain them.

The Britons were rescued from jail early this week by British troops using armor to crash through the prison walls. In a sign of continuing tensions and Iraqi fury over the British operation, Katyusha rockets were fired at U.S. and British facilities in the city Saturday, causing no casualties.

The major political development surrounded Abdel-Aziz al-Hakim, the head of the Shiite Supreme Council for the Islamic Revolution in Iraq. His appeal to voters added a key voice of support two days after Shiite Grand Ayatollah Ali al-Sistani also directed followers to back the charter.

“It is our religious duty to say ‘yes’ to the constitution and to go to the ballot boxes,” al-Hakim told more than 2,000 supporters gathered in Baghdad to mark a 1991 Shiite uprising brutally crushed by Saddam Hussein.

Al-Hakim said militants and former regime supporters were trying to undermine Iraqis’ hopes for security – but they would fail. His SCIRI organization has strong ties to Shiite Iran and controls a powerful bloc in parliament. Al-Hakim took refuge in Iran during Saddam’s rule.

Al-Sistani, meeting with aides Thursday in the holy city of Najaf, was the first major Shiite religious figure to urge voters to back the new basic law, according to two top officials in his entourage. The reclusive cleric issues statements only through his office and makes no public appearances.

In January, millions of Shiites heeded al-Sistani’s call to vote in Iraq’s first democratic elections in nearly half a century. The ballot gave the Muslim sect a majority in the new parliament and government.

Shiite solidarity is essential if the constitution is to pass in the Oct. 15 vote. If two-thirds of voters in any three of Iraq’s 18 provinces reject the document, a new government must be formed and the process of writing the constitution started over.

Minority Sunni Arabs are dominant in four provinces and could defeat the new charter should they vote “no” as a bloc in three of them. On Saturday, Sunni clerics and tribal leaders expressed optimism they could do just that while gathered at a meeting organized to scuttle the charter.

The three-day meeting, held in Amman, Jordan, for security reasons, ended with a communique urging a ‘no’ vote “if the constitution’s main points on Iraq’s unity and Arab identity are not rectified, as well as articles related to political and racial segregation.”