Sickness absence rates among council staff are at their highest since 1990, the local government auditor for Northern Ireland has said.

An average of 15 days were lost per employee during 2017-18.

Heavy reliance by some local authorities on agency workers increased the bill for temporary staff to £26m, the report said.

Auditor Pamela McCreedy said: "The monitoring and management of sickness absence levels continues to very challenging for councils.Staff welfare must be protected, along with the efficient and effectivedelivery of front-line services to the public.

"With no indication of overall improvement, I have decided that councils could benefit from a more detailed report in this area and I will work with thecomptroller and auditor general of the Northern Ireland Audit Office to commence a study in this area this year."

A smaller number of councils with enhanced powers have been created following a major shakeup of local government.

Absenteeism varied significantly between councils, with six reporting reduced absence levels from the previous year and five reporting increases.

Antrim and Newtownabbey Borough Council recorded the lowest number of days lost while Newry, Mourne and Down District Council recorded the highest.

Increases were attributed to a rise in long-term sickness absence because of conditions like severe depression, musculo-skeletal problems and stress.

Local councils employed the equivalent of more than 10,000 full time staff.They also spent £26m on agency workers, an increase of £1.7m from 2016/17.