The director of Ontario's police watchdog agency says it had a caseload approaching "record-high levels" in 2017 and investigators' work is becoming increasingly complex.

In the Special Investigations Unit's annual report, Tony Loparco says the agency opened 380 cases, which is an approximately 14 per cent increase over 2016.

The unit investigates incidents involving police where there has been death, serious injury or allegations of sexual assault.

Criminal charges were laid by the SIU against 20 officers in 18 cases in 2017, accounting for nearly five per cent of cases closed in that calendar year.

Loparco also praises the work of Justice Michael Tulloch, who recommended in a 2017 report that the police watchdog be fully independent from the government and have its powers expanded.

Legislation to increase SIU powers was recently paused by the new Progressive Conservative government, but Loparco says in the report he believes it will be implemented soon.