More than 70 people were wounded Monday when a Taliban truck bomber detonated a tonne of explosives outside a government complex in southern Afghanistan, the latest in a series of attacks that have sent civilian casualties surging.

Women and children were among those hurt in the explosion in the capital of Zabul province, Qalat, which ripped off the facades of government buildings and left scattered piles of rubble.

Separately, at least six civilians were killed late Monday when their pickup truck struck a roadside bomb in the Shahwalikot district of southern Kandahar province, officials said.

The violence comes as the Taliban step up attacks during their summer fighting offensive despite Kabul's repeated overtures to the insurgents to reopen peace negotiations.

Deputy provincial police chief Ghulam Jilani Farahi said 73 people, including six police officers and four members of the provincial council, were wounded in the attack on the Qalat complex, which houses several government buildings.

Zabul's police chief Mirwais Noorzai confirmed that more than 70 people were wounded, and said that four of them were in critical condition.

"Around 1,000 kilograms of explosives was used in the attack," he said.

The Afghan Taliban launched their annual spring-summer offensive -- titled 'Azm' (Determination) -- in late April, vowing nationwide attacks in what is expected to be the bloodiest summer in a decade.

The group, which has been waging a 13-year war against the US-backed Afghan government, admitted they were behind the Zabul attack although no one has claimed responsibility for the Kandahar roadside bombing.

"As part of the Azm operation, this afternoon a martyrdom-seeker... conducted an attack on the provincial council, where cruel and unjust decisions against Muslims and Islam were being taken," Taliban spokesman Qari Yousuf Ahmadi said in a statement.

Resolute Support, the NATO-led non-combat mission in Afghanistan, condemned the Zabul attack, saying in a statement it was "disgusted by the Taliban's complete disregard for human life".

The insurgents have launched a series of attacks in the capital and around the country as NATO forces pull back from the frontlines.

- Surge in attacks -

A blast triggered by a Taliban car bomber ripped through the parking lot of the justice ministry in Kabul on May 19, killing four people and wounding dozens of others.

Also this month 14 people -- mostly foreigners -- were killed in a Taliban attack on a Kabul guest house that trapped dozens attending a concert.

Official efforts to bring the Taliban to the negotiating table have so far borne little fruit.

The surge in attacks has taken a heavy toll on civilians, according to the United Nations Assistance Mission to Afghanistan. In the first four months of 2015, civilian casualties jumped 16 percent from the same period last year, it said.

The Afghan government has drawn public criticism for its inability to end insurgent attacks -- a fact partly attributed by critics to political infighting and a lengthy delay in finalising a cabinet.

President Ashraf Ghani on Thursday nominated Mohammad Masoom Stanekzai, a top official in the government body overseeing the country's peace process, for the crucial position of defence minister.

The post had been left vacant for months due to disagreements between Ghani and his chief executive officer and former presidential election rival, Abdullah Abdullah.

Public criticism over the failure to appoint a defence minister has been especially fierce.

Afghan forces are now solely responsible for security after NATO's combat mission formally ended in December, with a small follow-up force staying on to train and support local personnel.

Earlier this month NATO formally announced plans to retain a small military presence in Afghanistan after 2016 to help strengthen local security forces.
Source: AFP