The Maritime Self-Defense Force conducted exercises with the U.S. Navy on Friday amid North Korea’s continued nuclear and missile tests, the Defense Ministry said in a statement.

The show of naval muscle, which the ministry said began on Sept. 11 and was scheduled to wrap up on Sept. 28, involves the Ise, one of Japan’s two massive helicopter carriers, and the USS Ronald Reagan, an aircraft carrier based in Yokosuka, Kanagawa Prefecture, along with their escort ships.

The U.S. Navy’s 7th Fleet said the exercises saw the two navies carry out exercises involving air defense, anti-submarine warfare and sailing in formation.

South Korea’s Defense Ministry said earlier this week that its military would conduct a joint drill involving an aircraft carrier — likely the Reagan — next month.

The United States has ramped up bilateral exercises with its South Korean and Japanese allies, including a drill Monday that saw the U.S. military send four of its most advanced stealth fighter jets, along with two heavy bombers, for joint drills near Japan and over the Korean Peninsula in a “show of force” after the North launched a missile over Hokkaido on Sept. 15 for the second time.

Tensions have soared in East Asia as Pyongyang continues to resist growing international pressure to halt its ever-improving nuclear and missile programs, with U.S. President Donald Trump and North Korean leader Kim Jong Un trading increasingly menacing barbs.

On Friday, Kim delivered a scathing rebuke of Trump, calling him “mentally deranged” and vowing to make him “pay dearly” for threatening at the United Nations to “totally destroy” his country — a possible allusion to further weapons tests as the country’s top diplomat hinted that a hydrogen bomb test may be carried out over the Pacific Ocean.

“Action is the best option in treating the dotard who, hard of hearing, is uttering only what he wants to say,” he said, adding that Trump “will face results beyond his expectation.”

“I will surely and definitely tame the mentally deranged U.S. dotard with fire,” Kim said.

Trump responded over Twitter early Friday in Washington, saying: “Kim Jong Un of North Korea, who is obviously a madman who doesn’t mind starving or killing his people, will be tested like never before.”