KANDAHAR, Afghanistan - Two men on a motorbike gunned down an Afghan provincial official as he walked to work Wednesday in the main southern city of Kandahar, police said. Taliban insurgents claimed responsibility for the assassination.

The killing comes as NATO and Afghan forces move into the 12th day of a major offensive to push militants out of a Taliban stronghold in neighbouring Helmand province. The military alliance reported Wednesday that fighting was tapering off but bombs and gunmen continued to pose a threat.

Clearing roadside bombs and precautions to prevent civilian casualties have slowed the largest joint military operation since the ouster of the Taliban regime in 2001, which planners see as key to taking on the insurgents in their southern heartland and turning around the war.

Military officials have said the assault in Marjah is just the first push in a campaign that will move east into Kandahar province -- the Taliban's birthplace and where the hardline Islamist group still controls large swaths of territory.

Underscoring the threat militants pose, attackers shot and killed Abdul Majid Babai, the head of Kandahar's information and culture department, in the provincial capital then drove off, said Mohammad Shah Farooqi, the deputy provincial police chief. They have not been caught, he said.

Taliban spokesman Qari Yousef told The Associated Press that the insurgents were responsible for the killing.

Dozens of prominent politicians and religious leaders with ties to the Western-backed government have been killed in drive-by shootings or bombings in recent years, many in Kandahar city.

Babai had held his government post for about eight years and was not known to have stirred up controversy.

Reporting on the offensive in Marjah, NATO said in a statement Wednesday that fighting has tapered off over the 24 hours but bombs and gunmen "continue to pose a threat to civilians and security forces." Marine spokesmen have said militants are still shooting out of fortified bunkers.

Nevertheless, some residents have started to return, and NATO said a market in the north of Nad Ali district -- of which Marjah is part -- has opened for the first time in 18 months.

Protecting civilians has become a watchword of NATO's counterinsurgency campaign, boosted by extra U.S. forces sent by the Obama administration -- although the Marjah operation has also been marred by civilian deaths, including 12, at least five of them children, killed in a rocket attack that hit a house last week.

NATO commander Gen. Stanley McChrystal also apologized after Afghan officials reported an airstrike Sunday in central Uruzgan province -- which lies to the north of Helmand -- killed at least 21 civilians.

United Nations on Wednesday called on all sides to do their utmost to protect children from the conflict.

The UN says that while many more civilians are killed by militant bombs or attacks, new figures indicate that 131 children died in international airstrikes in 2009 -- slightly more than the 128 killed by militants, including those used as suicide bombers.

Another 22 children were killed in night searches by coalition forces, while 38 children were killed by undetermined perpetrators, the UN said.

"If there is going to be war then we would like the military on all sides to take measures to protect children," Rahika Coomaraswamy, the UN special representative for children and armed conflict, told reporters in Kabul.

She added, however, that she is encouraged by stricter rules of engagement adopted in recent months by NATO and hopes that will mean fewer children dying in 2010.