Riyadh: US Defence Secretary Jim Mattis looked to address confusion over a US aircraft carrier group on Wednesday, saying that its schedule had been disclosed earlier to be transparent.

"The bottom line is, in our effort to always be open about what we are doing we said that we were going to change the Vinson's upcoming schedule," Mattis told reporters, referring to the Carl Vinson strike group.

"We don't generally give out ships schedules in advance but I didn't want to play a game either and say we were not changing a schedule when in fact we had," Mattis said.

There had been confusion after US President Donald Trump boasted early last week that he had sent an "armada" as a warning to North Korea even as the aircraft carrier strike group he spoke of was still far from the Korean peninsula.