A teenage boy who was teaching English at a local school was dragged into the street and executed by Taliban militants, the provincial police chief reported.

The brutal killing sparked a clash that left two suspected Islamist fighters and two policemen dead, an official said.

"The boy, who was teaching English to other students after school hours, had been warned by the militants to stop teaching," provincial police chief Esmatuallh Alizai said.

Taliban militants have killed several teachers and students in the past for attending the government-run schools, which they regard as un-Islamic.

Officials on Friday said Afghan and foreign forces clashed with Taliban militants in southern Afghanistan, leaving 25 suspected insurgents and two policemen dead.

In southern Kandahar province, meanwhile, a roadside bomb hit a police patrol vehicle, killing four policemen, said Zhari district chief Niaz Mohammad Serhadi. Militants also opened fire on an SUV carrying two newlywed couples and their relatives, killing both couples and a child, said Kandahar provincial police chief Syed Agha Saqib. Another man and child were wounded.

In southwestern Nimroz province, a homicide bomber blew himself up next to a NATO convoy, but there were no casualties, said ISAF spokesman Maj. Charles Anthony.

The Associated Press contributed to this report.