Gunmen killed nine Afghan employees of a Czech aid organisation in an overnight raid Tuesday on their guesthouse in northern Afghanistan, officials said, the latest attack targeting humanitarian workers in the war-battered country.

No group has so far claimed responsibility for the killings in the relatively tranquil Balkh province, but the attack comes as the Taliban intensify their annual spring offensive despite repeated government attempts to reopen peace talks.

"Those killed in Zari district of Balkh province include seven aid workers -- six men and one woman -- and two guards," deputy provincial police chief Abdul Razaq Qaderi told AFP, blaming the Taliban for the attack.

The victims were employees of People in Need (PIN), a Czech organisation that has been active in Afghanistan since 2001, delivering humanitarian aid to remote communities in the east and north of the country.

"Unfortunately, last night unknown armed men attacked our guesthouse in Zari and martyred nine of our employees," a PIN official told AFP, requesting anonymity.

PIN condemned the attack, saying in a separate statement that it was "unprecedented in its brutality" and had prompted the organisation to immediately suspend all work in Afghanistan.

"Investigation is ongoing, the identity of the attackers is not known, but according to available information they did not originate from the area, where PIN has been working since 2002," the statement posted on their website said.

Employees of international aid organisations have increasingly come under attack in Afghanistan despite the Taliban espousing an official policy that rejects attacks on humanitarian workers.

The latest attack comes just weeks after 14 people -- mostly foreigners -- were killed in a Taliban attack on a guesthouse in downtown Kabul popular with international aid workers.

Five of them were Afghan employees of aid organisations including ActionAid and the Aga Khan Foundation.

In April, the bullet-ridden bodies of five Afghan workers for Save the Children were found after they were abducted by armed gunmen in the strife-torn southern province of Uruzgan.

"Afghanistan is one of the most challenging places for the humanitarian community with death, kidnappings and attacks against humanitarians all too frequent an occurrence," the UN's Afghanistan coordinator Mark Bowden said after that attack.

"I call on all parties to ensure that those providing humanitarian assistance have safe access to people in need and can carry out their life-saving work unhindered."

Last year a total of 57 aid workers were killed in Afghanistan, according to United Nations Assistance Mission in Afghanistan (UNAMA).

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.

President Ashraf Ghani's government has drawn criticism for failing to end growing insurgent attacks, which critics partly blame on political infighting and a lengthy delay in appointing a candidate for the crucial post of defence minister.

Ghani last month nominated Mohammad Masoom Stanekzai, a top official in the government body overseeing the country's peace process, for the job.

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