The United Nation mission in Afghanistan on Thursday voiced concern over a wave of violence including an air strike by NATO, resulting in dozens of civilians casualties.

Up to 18 people, including women and children were killed on Wednesday when a NATO air strike hit a house in Logar province south of Kabul.

The United Nations Assistance Mission in Afghanistan (UNAMA) has repeatedly expressed concern that aerial operations have resulted in more civilian deaths and injuries than any other tactic used by pro-government forces since the present armed conflict began, it said in a statement.

"The incident in Logar on 6 June reinforces this trend," it added.

Afghan president Hamid Karzai who is in Beijing for a meeting of the Shanghai Cooperation Organisation, a regional grouping led by Russia and China, also condemned the casualties as "unacceptable". He is cutting short his trip to return home.

The International Security Assistance Force (ISAF) however said "multiple insurgents" were killed in the air strike, which was ordered after troops were attacked "with small-arms fire and a grenade".

An ISAF spokesman later told AFP, after allegations of civilian deaths surfaced, that they were "assessing and gathering facts to try to determine what happened".

Civilian casualties caused by NATO have roiled relations between Afghanistan and the United States, which leads NATO forces in the fight against the Taliban.

Also on Wednesday dozens of civilians were killed and injured in a series of bomb and suicide attacks, claimed by the Taliban insurgent who have been waging a bloody insurgency since their ouster from power in late 2001.

In one of the deadliest incident a twin suicide bombing ripped through a crowded makeshift bazaar in southern Kandahar province killing 23 civilians and wounding as many as 50 others.

"These attacks produced the deadliest single day for civilian deaths in 2012. They also represent the worst day in civilian deaths since the Ashura (Muslim holy day) attack of December 2011 in Kabul," the UNAMA statement said.

For the past five years the number of civilians killed in the war has risen steadily, reaching a record of 3,021 in 2011, with the vast majority caused by insurgents, according to the United Nations.