KANDAHAR: A suicide truck bomb in southern Afghanistan on Tuesday killed two civilians and wounded more than 40, officials said, in the latest attack since the Taliban began their annual offensive.

The attacker detonated a lorry loaded with explosives at the gate of the police headquarters in Lashkar Gah, capital of the volatile Helmand province.

Afghan troops and police are battling the Taliban in the first “fighting season” since Nato ended its combat mission and left local forces to take charge of security.

The Helmand blast came less than two days after 11 soldiers were killed in a Taliban ambush in the normally relatively peaceful western province of Herat.

“It was a suicide truck bomber detonating his vehicle at the gate of police headquarters,” provincial police spokesman Farid Ahmad Obaid told AFP.

“Our initial reports show 40 wounded, two killed,” he said, adding that all of the casualties were civilians.

Provincial spokesman Omar Zhwak confirmed the attack.

“The blast was very powerful. Most of the wounded people are civilians who were hit by broken glass inside their homes,” he told AFP.

A doctor at the emergency hospital in Lashkar Gah said 40 civilians were brought to the hospital.

There was no immediate claim of responsibility for the attack. But the Taliban, who launched their annual spring-summer offensive in late April, vowed nationwide attacks in what is expected to be the bloodiest summer for a decade.

Read more: ISI officer involved in Kabul parliament attack, claims Afghan intelligence

Nato: coalition convoy targeted in suicide attack in Kabul

A suicide attacker driving an explosives-packed vehicle targeted a North Atlantic Treaty Organisation (Nato) military convoy in the Afghan capital, Kabul, on Tuesday, police and a Nato official said.

Police on the scene said casualties were expected.

"It was a suicide car bomber, there are casualties but it is too early to know the extent of the damage," said Kabul deputy police chief Sayed Gulagha.

A spokesman for the Nato mission in Afghanistan, US Army Col Brian Tribus, said that a coalition convoy had been attacked. “We can confirm there was an attack on coalition forces. We are gathering information,” he said.

The explosion happened at 1:20 pm on the main airport road in eastern Kabul. The blast sent a huge plume of black smoke over the city. It happened as government employees were leaving their offices and roads were choked with vehicles as the working day is shortened during the Holy month of Ramazan.

Huge explosion shakes Afghan capital near shopping district

A huge explosion shook the Afghan capital Kabul, sending a plume of black smoke over the city's western suburbs on Tuesday.

The cause of the explosion was not immediately known.

The Deputy Chief of Kabul police Sayed Gulagha has confirmed it was an explosion and says it appears to have occurred near a busy shopping district.

The blasts come a week after an audacious attack on the nation's parliament, which highlighted the ability of insurgents, who have been fighting to overthrow the Kabul government for almost 14 years, to enter the highly fortified capital to stage deadly attacks.

The Taliban's annual summer offensive has sent civilian and military casualties soaring and threatened major cities for the first time in a decade.

Read more: Taliban dissociate themselves from Afghan peace move

A fierce battle has been going on in the northern province of Kunduz, where last week Afghan forces recaptured a key district from Taliban fighters who had threatened to overrun their first provincial capital since being toppled from power in 2001.

Last week also saw the militants launch a brazen assault on parliament in Kabul, detonating a car bomb at the entrance and trading fire with security forces.

Police and soldiers beat back the attack with only two civilians killed, but the incident highlighted the Taliban's continuing ability to strike even at the heart of the heavily-secured capital.

Read more: Wars killed 149,000 in Pakistan, Afghanistan from 2001 to 2014