Corruption remains a serious obstacle to peace in Afghanistan, the UN said in its first report on the issue released Tuesday, in which it welcomed the government's efforts but said implementation is still a challenge.

The report, "Afghanistan's Fight Against Corruption: The Other Battlefield", cited positive anti-graft steps by the government, including the formation of an Anti-Corruption Justice Centre (ACJC).

But the fight "will not be won overnight", it said.

"Corruption has affected all aspects of life in Afghanistan, undermining public trust and confidence in government institutions, and hindering the country's efforts to become self-reliant," it stated.

Progress made "has been stymied by nepotism, political favouritism, and other external influences on recruitment decisions," the report continued.

"The president, for instance, recently observed that 150 civil servants in a single ministry were appointed without going through any merit-based review, and 95 percent of these appointees turned out to be related to or from the same ethnic group as the responsible minister," it said.

Afghanistan ranks a lowly 169th out of 176 countries in a corruption index released by Transparency International.

Graft permeates nearly every public institution, hobbling development despite hundreds of billions of dollars of foreign aid over the past decade, sapping already scant state coffers and fuelling insecurity as alienated Afghans veer towards the Taliban.

But since coming to power in 2014, President Ashraf Ghani, an American-educated former World Bank official, appears to have adopted a tougher stance.

Last May, he established the ACJC in an effort to bolster the legal system's ability to tackle corrupt ministers, judges and governors, who have largely been immune from prosecution.

The centre has since sentenced a number of mid-level Afghan government civilian and military officials, receiving praise in the report -- though it called on the government to work together to step up the fight.

"In many respects, the largest challenge in Afghanistan's fight against corruption is not the need to undertake additional reforms but, rather, the need to more effectively implement the reforms already undertaken," it said.

The report does not extend to security forces, undermined by nepotism, favouritism and ghost soldiers, who exist only on paper and whose pay is diverted.

But the head of the UN's mission in Afghanistan, Tadamichi Yamamoto, stressed during the report's release to the press that this was a critical sector that would be monitored closely by an international community hopeful for progress in 2017.