The head of the SIS is warning the threat of terrorism is growing.

Rebecca Kitteridge has made the comments in her agency's just published annual report.

She says the global terrorism threat has evolved alarmingly, both in terms of scale and mode of operation.

Ms Kitteridge is critical of the use of social media by terrorist groups to promote extreme ideology, believing it plants seeds in the minds of a very small minority of susceptible individuals.

Her report reveals 51 domestic intelligence warrants in force during the last financial year, up from 34 the preceding year.

They were in place for an average of 134 days