Suicide attackers Tuesday targeted foreign troops in Kabul and a police headquarters in restive southern Afghanistan, killing two people and wounding nearly 60, as the Taliban's bloody summer offensive showed no signs of letting up.

A powerful blast echoed around the Afghan capital as a suicide car bomber hit a convoy of foreign military vehicles on the main road to the airport, around 500 metres (550 yards) from the US embassy, wounding at least 17 people.

Hours earlier at least two civilians were killed when a suicide truck bomb detonated at the gate of the police headquarters in Lashkar Gah, the capital of 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.

Tuesday's violence 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 car bomber targeting a convoy of foreign forces in Kabul," interior ministry spokesman Sediq Sediqqi said.

A spokesman for the health ministry said initial reports showed at least 17 people were wounded in the Kabul blast, including women and children.

In Helmand, provincial police spokesman Farid Ahmad Obaid told AFP the police headquarters attack left at least two civilians dead and 40 wounded.

"It was a suicide truck bomber detonating his vehicle at the gate of police headquarters," Obaid told AFP.

Provincial police chief Nabi Jan Mullahkhil told reporters three attackers were involved.

"Two attackers were killed in the explosion while the third one was injured and as he tried to escape the police shot him,” he said.

Provincial spokesman Omar Zhwak confirmed the attack and said most of the wounded were hit inside their homes by flying glass.

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

- Bloody onslaught -

There was no immediate claim of responsibility for the attacks. 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.

After the Helmand attack a small blast hit a military vehicle in Kabul, police said, though there were no casualties.

"A small sticky bomb attached to a military vehicle detonated in western Kabul this morning. Only the car was damaged," Kabul police spokesman Ebadullah Karimi Kabul told AFP.

NATO’s combat mission formally ended in December after 13 years, but a small follow-up foreign force named Resolute Support has stayed on to train and support local security forces.

Stretched on multiple fronts and facing record casualties, Afghan forces are struggling to rein in the militants even as the government makes repeated efforts to jump-start peace negotiations.

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

A fierce battle has been going on in the northern province of Kunduz, where Afghan forces last week 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.