Seoul (TNA) – Three US aircraft carriers joined an ongoing exercise with the South Korean Navy in the East Sea on Sunday in an unprecedented show of force against a provocative North Korea.

The three flattops — USS Ronald Reagan, USS Nimitz, and USS Theodore Roosevelt — entered the operational area, called the Korea Theater of Operations (KTO), for the four-day maneuvers slated to end Tuesday, Yonhap news agency reported.

The KTO is an area that the commander of the South Korea-US combined forces is to zone off for military operations in case of a contingency. It can also involve open seas.

It marks the first time that three US aircraft carriers have joined together at close range for a joint exercise with South Korea, officials said.

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Seoul’s Joint Chiefs of Staff said that the maneuvers are aimed at enhancing the credibility of “extended deterrence” against the North’s nuclear and missile provocations. Extended deterrence refers to the US commitment to defend its ally by mobilizing all military capabilities, nuclear and conventional, against the North’s aggression.

“The combined drills are to present our resolve and will to deter North Korea’s provocations and retaliate if provoked,” a Seoul official said, declining to be named.

Apart from the nuclear-powered aircraft carriers, 11 US Aegis ships and seven South Korean warships, including two Aegis destroyers, participated in the drills.

The exercise comes after the two countries agreed in talks between their respective defense ministers last month to expand the rotational deployment of US strategic military assets to the Korean Peninsula to better cope with North Korean provocations.

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Seoul and Washington have recently carried out a series of drills to show off their military heft in response to the North’s saber-rattling, such as its sixth and most powerful nuclear test on Sept. 3 and a series of missile launches.

American leaders, including President Donald Trump, have warned the belligerent regime not to “underestimate” or “test” US strength.

This post originally ran on Tasnim News Agency.