A wave of suicide bombings in Afghanistan has killed at least 18 people, according to officials.

Three separate blasts in western Herat province and Musa Qala killed 10 policemen and eight civilians, as militants step up their activities at the start of spring fighting season.

In Herat, three policemen and eight civilians were killed when militants detonated a vehicle bomb as people queued to see a local politician.

Later on Tuesday, four policemen were killed after three suicide bombers attacked a police station in Musa Qala.

A further three policemen were killed and six more injured after another explosion in a nearby bazaar.

According to provincial spokesman Dawood Ahmadi, the attacks are symbolic of the Taliban's growing desperation.

They have lost their ability to fight face to face, so they are laying mines and carrying out suicide attacks. Local people are not letting them into their homes and villages, he told the BBC.

According to reports, police in Herat had received a tip-off about the bombing suspect, and were chasing the vehicle just before it exploded.

They were chasing the car and tried to stop it, police spokesman Raouf Ahmedi told the AP.

The vehicle then turned toward the district headquarters building and tried to pass the checkpoint, but police stopped them to be searched and asked where they were going.

Ahmedi added three people had been in the vehicle, including a woman wearing a burka.

The latest attacks come as fighters begin to emerge from their winter lull, when temperatures restrict movement.

Afghan forces have been in full control of Herat since July 2011, ahead of a 2014 pullout by all foreign combat troops.