BAGHDAD, Iraq (CNN) -- In one of the deadliest attacks in Baghdad in months, at least 51 Iraqis were killed and 75 were wounded Tuesday in a car bombing, an Iraqi Interior Ministry official said.

The bomb ripped through a garage and a bus stop, hitting an outdoor market and apartments, the official said. The blast in Hurriya, a predominantly Shiite neighborhood in northwestern Baghdad, was one of the deadliest to hit the Iraqi capital in months.

Prime Minister Nuri al-Maliki blamed it on "the defeated remnants of terrorism" and called it an attempt to revive the sectarian warfare that wracked the country for more than a year.

In a statement issued by his office, al-Maliki said "terrorists" and Islamic militants "returned to their old failing bet in trying to incite the sectarian strife" after defeats in Baghdad and other cities.

"This crime will not affect our determination and our commitment to fully defeat the terrorists and preserve the security triumphs achieved by the armed and security forces," the prime minister said. "This will add to our determination to rid the capital and the provinces from the remnants of the terrorists, murderers and criminals."

And U.N. Secretary-General Ban Ki-moon offered his "heartfelt condolences," his office said.

"The secretary-general condemns, in the strongest of terms, the terrorist bombing in northern Baghdad today which has reportedly killed over 50 people and left scores more injured," a U.N. statement said.

The blast came as officials tried to tamp down violence in Shiite areas, where U.S. and Iraqi forces have battled militias.

Earlier Tuesday, four civilians were killed in a suicide attack in northern Baghdad targeting a predominantly Sunni group opposed to al Qaeda in Iraq, an Interior Ministry official said.

The suicide attack is the latest in a flurry of strikes targeting the groups of predominantly U.S.-allied Sunni fighters known as the Awakening Councils or Sons of Iraq. Al Qaeda in Iraq is believed to be responsible for many of these assaults.

The suicide bomber was driving a motorcycle that struck a checkpoint in the predominantly Sunni Suliekh neighborhood. The four victims were Awakening members manning the checkpoint. Two others were wounded.

In other violence Tuesday, gunmen killed an employee of the Council of Ministers and wounded his father in western Baghdad, the Interior Ministry said. The man was driving and his father was in the passenger seat when gunmen in another vehicle shot them.

Also Tuesday, a bomb killed a municipal police chief in a volatile Shiite region south of Baghdad, police said.

Col. Saleh Mehdi Kuneihar, the chief of Aziziya, and another police officer were killed and two others were wounded when a roadside bomb struck their car on a road between Wasit and Diyala provinces.

Iraq's government battled Shiite militants in the southern city of Basra and Baghdad's Sadr City this spring.

The government is in the first stages of an operation in the southern province of Maysan, where Prime Minister Nuri al-Maliki announced a Wednesday deadline for "outlaws" to turn in in their weapons.

The move is al-Maliki's latest effort to stamp out militants and establish central governmental authority in the oil-rich southern region. Iraqi security forces also are fighting al Qaeda in Iraq militants in the northern city of Mosul.

Much of the fighting in Baghdad and Basra has been between Iraq security forces and members of Shiite cleric Muqtada al-Sadr's Mehdi Army militia.

Maysan province and its capital of Amara are believed to house Mehdi Army members who fled Basra and Baghdad after the earlier push.

Other developments

Gunmen killed an Iraqi journalist Tuesday in Mosul, police said. Muhieddin Abdul Hamid, an anchor for state TV's Nineveh channel, was slain by gunmen in a drive-by shooting outside his house.

An American-led coalition raid aimed at an al Qaeda in Iraq bombing network killed four "suspected terrorists" Tuesday in Mosul, the U.S. military said. Coalition troops approached a building and ordered people there to surrender; four militants were killed when they refused, according to the military.

At least 18 people were wounded Tuesday when a parked car bomb detonated near a police checkpoint in Baquba in Diyala province.

A U.N. refugee agency survey issued Tuesday said the Iraqi and Afghan conflicts have spurred an increase in refugees and the number of Iraqis internally displaced has grown. "After a five-year decline in the number of refugees between 2001 and 2005, we have now seen two years of increases, and that's a concern," said U.N. High Commissioner for Refugees Antonio Guterres. The number of refugees under the responsibility of the UNHCR rose to 11.4 million by the end of 2007, up from 9.9 million at the end of 2006, according to the annual report issued Tuesday. "Much of the increase in refugees in 2007 was a result of the volatile situation in Iraq," the agency said.

CNN's Jomana Karadsheh contributed to this report.

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