Two Iraqi election commission officials said Friday they have been detained after authorities reopened a corruption case against them, a move they dismissed as an effort to pressure the panel.

The move, while spotlighting the challenges Iraq faces in rooting out graft, threatens to fuel opposition charges that Prime Minister Nouri al-Maliki is seeking to consolidate power and suppress officials that do not go along with the government's agenda.

Faraj al-Haidari, chief of Iraq's electoral commission, said by phone that he is being held at a police station after a judge's decision to investigate old corruption allegations against the independent body.

Another member of the Independent High Electoral Commission, Karim al-Tamimi, said he was also detained.

Charges have not yet been brought against the men, who deny any wrongdoing. They were taken into custody on Thursday. The two spoke over cell phones to reporters.

"The allegations against us are baseless. The case is nonsense and is politically motivated," al-Haidari said.

Details of the detentions emerged as two separate ambushes killed seven Shiite pilgrims on their way to visit sites holy to the Muslim sect.

Gunmen opened fire on a bus destined for Samarra in the town of Tarmiyah, 30 miles (50 kilometers) north of Baghdad, killing five and wounding seven, police and hospital officials said.

Two other pilgrims were killed in Youssifiyah, about 12 miles (20 kilometers) south of the capital, as they were traveling by car to the sacred city of Karbala, according to authorities.

All of the officials providing details of the attacks spoke on condition of anonymity because they were not authorized to release the information.

IHEC is an independent government panel responsible for overseeing elections in Iraq. The elections body has often had to navigate a difficult course through Iraq's young democracy. Its members have been targeted by insurgents, and subject to death threats. Many travel only with bodyguards.

The nine-member board drawn from Iraq's various ethnic and sectarian factions also faces pressure from Iraq's numerous political factions. The members are appointed by the parliament.

The panel found itself in the middle of Iraq's most heated political debate in years after the recent parliamentary election in 2010. A Sunni-backed bloc narrowly won the most seats in the election. Although it was not enough to secure a majority, its strong showing was a surprise in the Shiite-dominated country.

As political factions scrambled to assemble support for a governing coalition, supporters of al-Maliki demanded recounts and complained the vote was plagued with fraud.

International observers called the vote and ballot count fair, and after a torturous recount also supervised by IHEC, the original results were widely found to be accurate.

But al-Maliki eventually kept his job after managing to form a broader Shiite coalition.

The allegations relate to payments given to employees of the government real estate registration department for plots of land given to IHEC board members.

Al-Haidari said the payments were made through official channels. "Everything was done legally," he said.

Earlier charges involving the payments were dropped.

A government anti-corruption body appealed that ruling, prompting the latest detentions, Supreme Judicial Council spokesman Abdul-Sattar Bayrkdar said. He added that the men have authority to give similar payments, also referred to as rewards, to IHEC employees, but not those in other government departments.

Al-Tamimi said he believes their detentions are meant to send a message that panel members should not continue their work _ essentially meaning the panel should hew more toward the government line. Al-Haidari said he suspected the detentions were payback for their perceived support of the Sunni bloc in the last elections.

Existing board members must have their positions renewed or face being replaced once their current terms run out next month, said Qassim al-Aboudi, another IHEC board member. He declined to comment on the detention of his colleagues.

The detentions follow the issuing of an arrest warrant in December against Tariq al-Hashemi, Iraq's top Sunni official. Al-Maliki's Shiite-dominated government accuses him of running death squads against Shiite pilgrims, government and security officials.

Al-Hashemi says those charges are politically motivated. He was in the northern Kurdish region when the arrest warrant was issued and has not returned to Baghdad. Al-Hashemi is currently out of the country.

Ali al-Moussawi, a media adviser for the prime minister, said the case involving the election officials should be left up to the courts.

"The government has nothing to do with it. The duty of the government is to support the Integrity Commission and its work," he said, referring to Iraq's anti-corruption watchdog. "Its duty is also to implement court decisions," he said.

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Associated Press writers Sameer N. Yacoub and Bushra Juhi contributed to this report.