Baghdad, Iraq ? Iraq will deploy thousands of police to prevent Sunni militants from bombing a major Shiite ceremony this week, while the bullet-riddled bodies of two Shiites were found Sunday in the latest round of killings between rival Sunni and Shiite groups.

The U.S. military, meanwhile, announced the release of about 50 Iraqi detainees, but no women were among them. The freeing of women is a demand by kidnappers of American journalist Jill Carroll, who was abducted Jan. 7 in Baghdad.

Sectarian anxieties are running high in Iraq amid a spate of killings and kidnappings. The violence threatens talks to form a national unity government, which the U.S. hopes will bring the country’s main Shiite, Sunni Arab and Kurdish parties closer together and end the bloodshed.

Three gunmen shot dead two policemen in the northern city of Kirkuk, and a roadside bomb killed two civilians in Madain, about 14 miles southeast of Baghdad, police said. Five civilians and two policemen were also wounded in the Madain blast, which targeted a passing police convoy.

Amid the tensions, Iraqi forces are stepping up security ahead of the most important date in the Shiite calendar – the feast of Ashura – to prevent a repeat of suicide bombings by Sunni extremists that killed at least 230 people during the ceremonies in the past two years.

Ashoura, which falls this year on Thursday, marks the 7th century death of the revered Shiite saint Imam Hussein, grandson of Islam’s Prophet Muhammad. Hundreds of thousands of Iraqi Shiites are expected to take part in ceremonies, including self flagellation, in a show of grief to mark Hussein’s death in battle.

Ceremonies have already begun but will reach their climax Thursday.

Interior Ministry Undersecretary Maj. Gen. Ahmed al-Khafaji said Iraqi police forces will be on high alert to prevent a repeat of previous Ashura-linked terror attacks claimed by al-Qaida in Iraq, a group headed by Jordanian-born militant Abu Musab al-Zarqawi.

“The attacks that happened on Ashura during the previous years gave us more insight about what measures we should take to prevent the repetition of the same attacks,” al-Khafaji told The Associated Press.

Extra checkpoints and police patrols will be operating in major Shiite centers such as the holy southern cities of Karbala and Najaf and predominantly Shiite areas in Baghdad such as the northern suburb of Kazimiyah.

At least 8,000 police will be on duty in Karbala, where security authorities have warned hotel owners not to accept any non-Iraqi Arabs or Iraqis without identity documents and to inform authorities about suspicious individuals, said police spokesman Abdul Rahman Mishawi.

Ashoura falls on the 10th day of Muharram in the Islamic calendar and is the holiest festival for Shiites, who comprise 60 percent of Iraq’s 27 million people.

It marks the anniversary in the Islamic lunar calendar of the death of Imam Hussein, who was killed in 680 A.D. during a battle in Karbala for leadership of the faith. Hussein’s death caused the split in Islam between Shiites and Sunni Muslims.