An UN official said Monday he was " saddened" by the death of 27 civilians by a mistaken airstrike launched by NATO-led International Security Assistance Forces ( ISAF) in S. Afghanistan on Sunday night.

"I am deeply saddened at the reports of the terrible loss of civilian life on Sunday in southern Afghanistan," said Robert Watkins, Deputy Special Representative of the Secretary-General for Afghanistan, in a statement issued Monday night.

"UNAMA has consistently requested all parties to the conflict to do their utmost to avoid civilian casualties," he added.

"Measures highlighted in the tactical directives and guidelines issued by ISAF on the use of lethal force must be fully implemented at all times and under all circumstances," he further said.

An NATO air strike against suspected Taliban militants in the southern province of Dai Kondi on Sunday left 27 civilians, including four women and a child dead, and injured another dozen, according to a statement issued by the Afghan Presidential Palace.

The country's cabinet, while previously put the number of casualties at 33, in a sharp reaction strongly condemned the incident, calling on NATO-led troops to avoid harming innocent citizens.

General Stanley McChrystal, Commander of NATO and U.S. troops in Afghanistan, had expressed his sorrow and regret to Afghn President Hamid Karzai, and pledged to fully partner with the joint investigation, according to a statement by the NATO troops.