Iraq's president sought to calm rising pre-election tensions Thursday, pushing for a legal ruling on whether a political vetting panel had the right to blacklist hundreds of candidates for suspected links to Saddam Hussein's Sunni-led regime.

The proposed ban has muddied preparations for parliamentary elections March 7 and raised fears that U.S.-backed efforts to promote national unity could be undermined.

Vice President Joe Biden is expected to visit Baghdad soon, underscoring Washington's concern about the flare-up between the Shiites who claimed wide control of Iraq after Saddam's fall and Sunnis who seek a greater say in Iraq's decisions.

The friction was on display in Iraq's Shiite-dominated south, where protesters Thursday beat campaign posters with shoes — a deeply insulting act in the Arab world — and set them alight while chanting slogans including "No to Baathists" in a reference to Saddam's Sunni-dominated Baath party.

President Jalal Talabani said the three-member presidential council he leads has sent a letter to the head of the Higher Judicial Council requesting a ruling after the vetting committee banned 511 candidates in a move that threatens to cast a shadow over the vote.

"I, myself, am not satisfied with the banning decision," said Talabani, a Kurd who has strongly backed reconciliation between Iraq's main Shiite, Sunni and Kurdish groups. He told reporters he was seeking a ruling on "whether this committee that issued the decision is legitimate or not" because it does not have full parliamentary backing.

The government-sanctioned body behind the ban — the Accountability and Justice Committee — is tasked with weeding out from the government and security forces hardcore supporters of Saddam's outlawed Baath party. Like the government, the committee is dominated by Shiite Muslims and its decisions are seen as biased against the once-dominant Sunni Arab minority that prospered under Saddam.

A predecessor of the committee was known as the de-Baathification Commission and was created by U.S. occupation authorities following the American-led, 2003 invasion of Iraq. That panel faced Sunni charges that it acted with excessive zeal in purging Baathists, many of whom had joined the party to promote their careers or protect themselves from the regime.

Critics say the purges have robbed the civil service, academic institutions and the armed forces of some of their best and most experienced employees, and created the chaos afflicting government departments to this day.

There is also the difficult challenges of trying to distinguish the hard-core Saddam sympathizers from those who supported the Baath Party to preserve jobs and gain official favors. Such lines have been blurred by blanket charges by Prime Minister Nouri al-Maliki that blame Baathists for recent bombings in Baghdad, including a series of blasts in December that killed more than 125 people.

The current committee has not escaped criticism either. It is led by Ali al-Lami, a Shiite once detained by the U.S. military over a 2008 attack in a Shiite district of Baghdad. The attack targeted U.S. forces and was blamed on Shiite militiamen.

Al-Lami himself is running in the March election, a fact that has raised questions about the motive behind the bans.

Some Sunnis accuse al-Lami and other Iraqi Shiites of being too close to Shiite powerhouse Iran and its policies, which include heavy vetting of candidates on ideological grounds before presidential and other elections.

The legal challenge raised by Talabani is expected to focus on whether the current panel has legal authority since its membership was not confirmed by a parliament vote.

Washington hopes the March election will be a significant step toward reconciliation between the majority Shiites and the once-dominant Sunni minority, and will help cement substantial but still tenuous security gains. American troops are expected to accelerate their withdrawal from Iraq soon after the election.

Violence remains a problem, as highlighted by attacks across Iraq on Thursday.

Gunmen killed an Iraqi army colonel near his house in the country's north, marking the third deadly attack in a day on members of security forces in and around Mosul. The victim's cousin, Nafaa Khudir, identified the officer Thursday as Col. Salih Ahmed al-Ukaydi of the Iraqi Army's 2nd division. Police confirmed the attack.

The shooting came hours after two off-duty policemen were killed in Mosul.

South of Baghdad, a roadside bomb killed one policeman and wounded four others, according to Babil provincial police spokesman Maj. Muthana Khalid.

In Iraq's predominantly Shiite southern city of Basra, about 200 protesters poured into the streets to support the proposed ban on candidates with Baathist ties. Similar demonstrations drew hundreds in the mostly Shiite cities of Najaf and Kut, where one banner read: "Death to Baathists."

Meanwhile in Baghdad, a British security contractor accused of shooting two colleagues to death appeared briefly in court, where the judge accepted a defense request to have him examined by a medical and psychological committee, his lawyer said.

The contractor, Danny Fitzsimons, is accused of shooting two colleagues, a Briton and an Australian, during a fight in Baghdad's heavily fortified Green Zone in the summer. All three men were working for the British security firm ArmorGroup Iraq.

Fitzsimons' defense team argue he is suffering from mental anguish caused by his military service in Iraq.

Fitzsimons would be the first Westerner to face an Iraqi trial since a U.S.-Iraqi security pact that took effect just over a year ago lifted immunity for foreign contractors.

The trial has been adjourned until Feb. 18, according to Fitzsimons' attorney, Tariq Harb.