Suicide bombers have killed at least 15 people in two separate attacks in western and southern Afghanistan, raising fears of a renewed spring offensive by insurgents.

Officials say at least 11 people were killed, including three policemen, in a suicide car bombing outside a local government facility near the capital of the western province of Herat.

The militants, who were being pursued by police, detonated their explosives after being told to stop their vehicle on an airport road in Guzara district. Officials say one of the bombers was wearing a burqa.

At least 23 people were wounded in the attack.

Hours later, officials in the southern province of Helmand said at least four policemen were killed when three bombers stormed a police compound in the district of Musa Qala. The police commander was wounded in the attack.

Two of the assailants were able to set off their explosives, while a third was shot dead by police.

The Associated Press reports that the Taliban has claimed responsibility for both attacks.

Herat province, which borders Iran, is normally relatively peaceful, with most insurgent attacks concentrated in Afghanistan's south and east.

Observers are concerned the Taliban may attempt a repeat of last year's spike in violence during the warmer spring months, which saw several high-profile attacks on Afghan and foreign bases.

NATO troops have already transferred security control of large portions of Afghanistan to local authorities. All foreign combat troops are scheduled to leave the country by the end of 2014.