Nine Afghan employees of a Czech aid organisation were killed in an attack on their guesthouse in northern Afghanistan, officials said.

An official from the northern Balkh province told Al Jazeera that the gunmen attacked the compound of the NGO in Zari district.

The victims included seven aid workers - six men and one woman - and two guards, local officials told Al Jazeera, blaming the Taliban for the attack.

The victims were employees of People in Need (PIN), a Czech organisation which has been delivering humanitarian aid around Afghanistan since 2001.

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

No group has so far claimed responsibility for the killings but the attack comes as the Taliban intensify their annual spring offensive despite repeated overtures from the government about reopening peace negotiations.

International aid workers 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.

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 the 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 officer and former presidential election rival, Abdullah Abdullah.