Twin car bombs exploded minutes apart in a busy Shiite marketplace, and two minibuses exploded in separate attacks across Baghdad Sunday - killing at least 37 people, police and hospital officials said.

North of the capital, two British helicopters crashed after an apparent collision in air, killing two service members, UK officials said.

Sunday's bombings were a renewal of sectarian carnage in the capital, and a setback in the more than two-month-old US push to pacify Baghdad.

The attacks came a day after insurgents exploded a bomb close to one of Shi'ite Islam's holiest shrines in Karbala. The city's health department Sunday revised its death tolls from the attack, saying 47 people were killed and 224 injured.

The two British helicopters crashed after an apparent collision 19 kilometers north of Baghdad, killing two British personnel. Four other personnel were injured in the crash.

"An investigation will be conducted to determine the cause of the incident; however, initial reports indicated it appears to be from a mid-air collision and not the result of enemy fire," the US military said in a statement.

Later, UK Defense Secretary Des Browne said the helicopters and casualties were British, and that initial reports suggested the crash was an accident.

"Sadly, two personnel have died and one is very seriously injured. All of these were UK personnel. My thoughts and sympathy are with them and their families," Browne said, adding that the next of kin had been informed.

The initial US statement referred to the downed helicopters as "coalition", but officials later said they were investigating reports that they were British instead of American. British forces, headquarters in the southern city of Basra, rarely fly missions north of Baghdad, where the helicopters crashed.

"I can't talk about the particular mission they were involved in, but we do have units operating as part of the coalition across Iraq," a British defense ministry official said on condition of anonymity, in line with government policy.

(China Daily via agencies April 16, 2007)