(Adds comment from U.N. chief envoy in Iraq, paragraph 6)

By Dean Yates

BAGHDAD, Jan 21 (Reuters) - A suicide bomber killed 15 people and wounded 10 others on Monday at a funeral near the volatile northern Iraqi oil refinery city of Baiji, security officials said.

It was the latest in a spate of suicide bombings in northern Iraq, where U.S. and Iraqi forces have launched a major operation to drive out al Qaeda militants. The Sunni Islamist group is seen as responsible for most suicide attacks in Iraq.

The bomber walked into a funeral tent for a local tribal leader and blew himself up among mourners, who included Salahuddin provincial government officials and members of a local U.S.-backed anti-al Qaeda Awakening Council.

"There was a big explosion. The tent was filled with the body parts of mourners. No one can be identified," said one survivor, Ahmed Abdullah, a Salahuddin government official.

Funeral tents have frequently been targeted in Iraq's sectarian bloodletting between majority Shi'ites and minority Sunnis because it is easy for suicide bombers to mingle among mourners without being noticed.

The attack came as the United Nations' chief envoy in Iraq gave a mixed report to the Security Council in New York on the country's situation.

Staffan de Mistura said security had improved, but that Iraqi political consensus was needed for a long-term reduction in violence.

The head of the U.N. Assistance Mission for Iraq (UNAMI) told the council the reasons for the reduced level of violence include the increased presence of U.S. and other troops, a ceasefire declared y Shi'ite cleric Moqtada al-Sadr's Mehdi Army militia and increased cooperation with Iraq's neighbours.

Monday's attack took place in al-Hajaj village, 5 km south of Baiji, home to Iraq's biggest oil refinery. The city, 180 km (112 miles) north of Baghdad, has been the scene of a number of bombings in the past few months.

On Dec. 25, a suicide bomber killed more than 20 people in the city.

The commander of U.S. forces in northern Iraq, Major-General Mark Hertling, said last month that al Qaeda was regrouping in the north after being pushed out of Baghdad and western Anbar province and was still capable of launching "spectacular attacks".

AIR STRIKES

While overall levels of violence in Iraq are sharply down, there has been a slight increase in the number of suicide bombings since last October, U.S. military data shows.

The U.S. military says al Qaeda is the greatest threat to peace in Iraq and launched a ground and air offensive against the group in four northern provinces, including Salahuddin, and Baghdad's southern outskirts on Jan. 8.

U.S. warplanes dropped 30,000 pounds of bombs on a suspected al Qaeda safe haven south of Baghdad, the U.S. Air Force said, the latest in a series of air strikes aimed at disrupting the Sunni Islamist group's operations.

The U.S. Air Force said the operation, which began on Sunday night and continued on Monday morning, involved B-1 bombers and F/A-18 jets. It targeted Salman Pak, an area 35 km south of Baghdad.

In a separate statement, the U.S. military said warplanes had dropped 35 bombs on 30 al Qaeda targets on Sunday in Arab al-Jabour, an area of date palm groves on Baghdad's southern outskirts. It was not immediately clear whether it was part of the same operation outlined by the Air Force.

The U.S. military says it is trying to keep al Qaeda militants on the run, making it difficult for them to plan and carry out attacks. But military analysts say the group has repeatedly proven itself flexible and resilient.

U.S. military spokesman Rear Admiral Greg Smith said on Sunday 121 militants had been killed, including 92 "high value" targets so far in the offensive, called Operation Phantom Phoenix.

Smith said al Qaeda had killed 3,870 civilians and wounded almost 18,000 in 4,500 attacks in 2007. (Writing by Ross Colvin; Editing by Matthew Jones)

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