The Afghan Taliban has denied that its leader Mullah Omar has died, saying a text message announcing his death was a fake.

A Taliban spokesman said Wednesday the message was sent after the group's phones and website were hacked, and blamed U.S. intelligence agencies.

Omar has been reported dead before, including in March when an Afghan news channel said he had been killed by members of Pakistan's spy agency.

The one-eyed Afghan Taliban leader has a $10 million bounty on his head. He led Afghanistan during the 1990s, establishing strict Islamist rule under which girls were banned from going to school.

Also Wednesday, officials in southern Afghanistan said militants killed at least three policemen during a gunbattle in the city of Kandahar, including the district police chief. Two militants were also killed in the clash.

In the northern city of Mazar-i-Sharif, a bomb planted on a bicycle killed at least four civilians, including a child, and wounded at least 10 others.

The attack comes as Afghan forces prepare to take security control of the city from NATO troops, as one of several areas set to transfer to Afghan control this month.

U.S. forces have already handed over control of Bamiyan province and the relatively peaceful city of Mehterlam in eastern Laghman province.

The transfers are the first phase of a plan that will see all of the country's security under Afghan control in the next three years.

International combat troops are set to completely withdraw from Afghanistan by the end of 2014.

Security control of Lashgar Gah, the capital of southern Helmand province, is set to be handed over to local troops this week.

Violence has increased in Afghanistan since President Hamid Karzai announced the first phase of the security transition.

Despite the violence, the Afghan government official who heads the transition process said Tuesday that Afghan forces were fully capable of handling security in the seven areas to be transitioned first.