United Nations peacekeepers should use force more frequently to protect civilians under attack but often fail to do so because they are afraid of court action, an internal report said.

The evaluation by the UN's Office of Internal Oversight Services noted a reluctance to deploy force -- even when it had been authorized by the United Nations Security Council.

A perceived lack of staff or equipment, and the threat of being court-martialed or prosecuted before the International Criminal Court, were among factors preventing peacekeepers using force in hot spots including South Sudan.

Of 507 incidents involving civilians between 2010 and 2013, only 20 percent "were reported to have attracted an immediate mission response," the report said.

"In cases where response was reported, missions almost never used force, even as a last resort."

Responding to the report, UN peacekeeping chief Herve Ladsous said there needed to be more focus on "comprehensive political solutions."

"We also regret that the study did not highlight the central role host nations play in the protection of civilians," he added.

The report, dated March, was presented this week to a UN General Assembly committee charged with overseeing the organization's budget.

The report is based on evaluation of eight of 10 UN peacekeeping missions charged with protecting civilians, including those in the Democratic Republic of Congo, South Sudan, Haiti, and the joint UN-African Union mission in Darfur.