Two car bombs in the capital killed 13 Iraqi soldiers and wounded dozens in the latest attacks targeting Iraq's security forces.

Judge Barawiz Mahmoud and his son, who worked as a lawyer, were shot dead as they left their home in northern Baghdad on Tuesday.

"He was working in the special tribunal. He was involved in cases including Saddam's," one ministry official said.

It was not clear whether his killing was connected to his work at the tribunal, and police said they were investigating.

It was the first assassination of a member of the special tribunal, which includes around 50 trial judges, investigating magistrates, prosecutors and appeals court judges.

The killing came a day after the tribunal referred its first charges against defendants, saying it had enough evidence to put five former Baath party officials on trial, including Saddam's half brother Barzan Ibrahim al-Hassan al-Tikriti and former Deputy Prime Minister Taha Yasin Ramadan.

The trial is not expected to begin for at least another seven weeks. Saddam, who briefly appeared before a judge last July, is expected to be tried next year on war crimes charges.

Iraqi officials involved with the special tribunal say they hope the trials of Saddam's top deputies will help build a case against the former dictator, captured in December 2003.

One of Wednesday's car bomb blasts in Baghdad was outside an Iraqi army base used as a recruitment center. Six soldiers were killed and 38 people were wounded, police said.

A second car bomb targeted a convoy of Iraqi soldiers, killing seven and wounding two, police said.

Guerrillas fighting to overthrow the US-backed government have repeatedly attacked Iraqi police and soldiers, as well as people queuing up to recruit in the security forces.

On Monday, a suicide car bomb attack on Iraqis hoping to join the police in Hilla, south of the capital, killed 125 people -- the deadliest single attack since Saddam's overthrow.

al-Qaeda's wing in Iraq, led by Jordanian militant Abu Musab al-Zarqawi, claimed responsibility for the Hilla blast. Washington says Zarqawi is its top foe in Iraq and is offering $25 million for information leading to his death or capture.

General John Abizaid, head of US Central Command, told the Senate Armed Services Committee that improved Iraqi intelligence sources and "treason within his own organisation" had led to successes against Zarqawi.

"His days in Iraq are numbered," Abizaid said.

He said that on Iraq's election day on Jan. 30, when Zarqawi sent suicide bombers to attack polling stations, only around 3,500 insurgents took part in efforts to disrupt the poll.

"And we say to ourselves: 'Why didn't they put more people in the field? Where were they?' They threw their whole force at us, we think, and yet they were unable to disrupt the elections because people wanted to vote," Abizaid said.

He said the number of insurgents was falling because of Iraq's progress toward democracy.

"I think that the voting in Iraq, the political process that's going on in Iraq, the fact that people of moderate disposition have a chance for a better future, have driven those numbers down," Abizaid said.

An alliance of mainly Shia Islamist candidates won by far the most votes in the elections, confirming the political dominance of the Shia majority after decades of oppression under Saddam's Sunni-dominated government.

Many Sunni Arabs boycotted the polls or were too afraid to vote, and the 20 percent Sunni Arab minority has little representation in Iraq's new parliament, sparking concerns that sectarian tensions will fuel violence.