Some 90 civilians, including 60children, were among those killed during military operation in the strife-torn Afghanistan's western Herat province last week, a United Nations investigation has revealed.

The investigation was conducted by a team of human rights officers from the United Nations Assistance Mission in Afghanistan (UNAMA) which had gone to Herat following reports that a large number of civilians were killed by foreign and Afghan military personnel around midnight on August 21.

The UN said the team found "convincing evidence, based on the testimony of eyewitnesses, and others," that some 90 civilians were killed - including 60 children, 15 women and 15 men - and another 15 villagers wounded.

"This is a matter of grave concern to the United Nations. I have repeatedly made clear that the safety and welfare of civilians must be considered above all else during the planning and conduct of all military operations," Kai Eide, Special Representative of the Secretary-General for Afghanistan, said in a statement issued on Wednesday in Kabul.

According to the people interviewed by UNAMA, the military operations lasted several hours during which air strikes were called in.

"The destruction from aerial bombardment was clearly evident with some 7-8 houses having been totally destroyed and serious damage to many others. Local residents were able to confirm the number of casualties, including names, age and gender of the victims," the mission said.

Eide called on the international and Afghan military forces to "thoroughly review" the conduct of the operation to ensure that it does not happen again.

"The impact of such operations undermines the trust and confidence of the Afghan people in efforts to build a just, peaceful, and law-abiding state," he stated, reminding all parties that the protection of civilians must be their primary concern.

Meanwhile, the head of UNAMA's human rights unit has expressed deep concern that two individuals convicted in 2006 for the rape of a woman in Samangan province in northern Afghanistan have been released early from detention.

"This sends the wrong message to other perpetrators of violent crimes against women, that they will not be held accountable for their actions," said Norah Niland, adding that "there can be no peace in Afghanistan without justice."

Niland noted that the 11-year prison sentence against the perpetrators was upheld by the Court of Appeal and confirmed by the Afghan Supreme Court.

However, the two men were subsequently released from incarceration after serving "a fraction of their sentence" and are now back in the neighbourhood where the crime was perpetrated and where the victim and her family continue to live.

"While there appears to be conflicting reports on the circumstances of the release of these prisoners, whatever the circumstances, this is clearly an injustice against the victim, the victims' family and all Afghan women," Niland stated.

"Such injustice can only promote a culture of impunity for violence perpetrated against women," Niland added.

She welcomed the intention by the Afghan authorities to investigate the circumstances surrounding the release.