A policeman stands guard at the scene of a bomb attack in Kirkuk, about 155 miles north of Baghdad, July 16, 2007. [Photo: Reuters]

At least 85 people were killed on Monday by a suicide truck bomb in the volatile Iraqi city of Kirkuk, some of them trapped on a bus where they burned to death, a witness said.

Police also said 180 people were wounded in a blast that heightened tension in the oil-producing northern city, shared by Kurds, Turkmen, Shi'ite and Sunni Arabs. The city plans to hold a crucial referendum later this year on its future status.

"Tens of houses and shops were totally destroyed by the power of the explosion," said General Torhan Abdul Rahman, the city's deputy chief of police.

Dozens of cars were set on fire and Reuters pictures from the scene showed a number of charred and torn bodies in the bus and a large crater in the road where the truck blew up. A police pick-up was splattered with blood.

U.S. and Iraqi military operations in and around Baghdad have reduced the number of particularly big attacks in the capital in recent weeks. But violence has flared elsewhere in the country, where security forces are more thinly spread.

Kirkuk is not far from Tuz Khurmato, where a massive truck bomb in a crowded market killed at least 130 on July 7, in one of the deadliest single insurgent attacks since the 2003 U.S.-led invasion of Iraq.

Adnan Sarhan, 30, lost both his eyes and had his back broken in the Kirkuk explosion. He was being operated on while his distraught mother waited for news.

"Will I ever see my son alive again," asked Mahiya Qadir, 70, sat anxiously near the surgery with her daughter-in-law.

The blast, near an office of the Patriotic Union of Kurdistan of Iraqi President Jalal Talabani, was one of several attacks in Kirkuk, which is supposed to vote to decide the status of the city later this year.

Kurds want it to join the semi-autonomous region of Kurdistan but many other residents prefer that it remain under the wing of the central government in Baghdad.

BURIED BODIES

"I was sat in my office and all I saw were the walls and roof collapsing on me," said PUK officer Kawa Ibrahim.

Police said there were at least 25 critically injured and many bodies might still be buried in the rubble.

More than 20 survivors were also rushed to Salaimaniya in Kurdistan for treatment, a doctor there said, warning many needed amputations or other major surgery.

The truck detonated minutes apart from a car bomb in a busy Kirkuk shopping area that wounded two people, police said.

A police officer was killed and four officers were wounded soon after, when a parked car bomb exploded in southern Kirkuk, police said. A fourth car bomb was discovered and made safe.

South of Baghdad, thousands of U.S. troops swooped on a suspected al Qaeda in Iraq safe haven used to reinforce militants fighting in the capital, the military said.

U.S. and Iraqi forces have launched a series of big security clampdowns since the last of 28,000 extra U.S. troops ordered to the country by U.S. President George W. Bush arrived last month.

They aim to thwart violence between majority Shi'ites and minority Sunni Arabs which has pushed Iraq towards civil war, while winning time for Shi'ite Prime Minister Nuri al-Maliki to deliver key power-sharing laws.

Time is pressing. Many Americans want their soldiers to come home soon and senior members of Bush's own Republican Party have broken ranks to call for a change of war strategy.

Bush says he will not alter course before a September review to U.S. lawmakers from General David Petraeus and Ambassador Ryan Crocker, his top two personnel in Iraq.

Monday's operation, called Marne Avalanche, aims to stem the flow of weapons and militants into the capital, where U.S. and Iraqi forces are already fighting to clear them out.

In pre-dawn raids, helicopter-borne troops swept into an area the U.S. military said was an al Qaeda safe haven around the Euphrates river valley, 35 km (22 miles) south of Baghdad.