Afghan officials said Wednesday at least 12 policemen were killed or wounded in two separate Taliban attacks on checkpoints.

Authorities said that in the first incident southwest of Kabul, six policemen were killed in an early morning gunfight.

Hours later, at least six policemen were killed or wounded when a suicide bomber blew himself up at a checkpoint in central Ghazni province. Clashes erupted between insurgents and police after the bombing.

In other violence, two NATO soldiers were killed Wednesday in two separate insurgent attacks in the country's south and east.

The Taliban has stepped up its attacks on government officials and Afghan and international troops in recent months.