Spencer, who met with representatives of all medical groups last Friday, said payments were being authorised by people who were not designated to do so.

"I want to ensure that if this is so, then it is corrected immediately," he said.

He said the investigation was not a witch-hunt and was not aimed at targeting any particular group of workers.

The investigation follows allegations by the chief medical officer, Dr Sheila Campbell-Forrester, early last month that some health workers were benefiting from a $1-billion arrangement set aside for on-call duty payments during the malaria outbreak in late 2006 and early 2007.

Campbell-Forrester alleged that there were health workers who had been paid even when they had not performed any extra duties.

The comment made nurses irate and they demanded an apology from the chief medical officer.