The United States and South Korea have started joint naval drills that will involve three US aircraft carriers in what military officials describe as a clear warning to North Korea.

The four-day drills that began on Saturday in waters off South Korea’s eastern coast come as President Donald Trump continues a visit to Asia that has been dominated by discussions over the North Korean nuclear threat.

South Korea’s military says the battle groups of the USS Ronald Reagan, the Theodore Roosevelt and the Nimitz will successively enter the exercise area during the drills that run until Tuesday.

The three carriers will be likely together in the drills around Monday.

It’s the first time since 2007 that three US carrier strike groups are operating together in the Western Pacific.