The International Maritime Security Construct (IMSC) is celebrating a big drop in "state-sponsored malign activity" in and around the Strait of Hormuz in the year since it began operations.

The nine-member, US-organised security coalition said on Tuesday that thousands of hours of patrols have helped keep commerce moving in the politically sensitive and economically critical region.

"Since the inception of the IMSC there have been no attacks on IMSC-lagged vessels," said UK Royal Navy Commodore Rob Bellfield, who took command in April.