The Maritime Self-Defense Force has begun joint drills with the aircraft carrier USS Carl Vinson and its escort vessels in the Western Pacific, the Defense Ministry said Sunday, as the U.S. strike group crept closer to the Sea of Japan.

The MSDF destroyers Samidare and Ashigara, which departed Sasebo naval base in Nagasaki Prefecture on Friday morning, are taking part in the exercises amid concerns that North Korea is preparing to conduct more missile and nuclear tests this week.

An MSDF spokesman told The Japan Times on Sunday that the drill was not based on any specific combat scenario and that “no particular country was in mind” when the drill was planned.

The Japanese destroyers will practice cruising in tactical formation and test communications procedures with the U.S. ships during the drill, the official said.

“The MSDF always looks for opportunities to conduct joint drills with the U.S. Navy, and we consider this good timing” since the Vinson is coming to the Western Pacific, said the official, who declined to be named.

The official said the MSDF has not decided when the drills will wrap up.

In a statement, the U.S. Navy said the drills took place in the Philippine Sea.

“We always look forward to operating with our Japanese partners,” Rear Adm. Jim Kilby, commander of the strike group, said in the statement. “The relationship between the JMSDF and the United States is better than ever and it’s in part thanks to these bilateral exercises.”

In Washington late Saturday, the White House announced that U.S. President Donald Trump was to hold telephone talks with Prime Minister Shinzo Abe early Sunday, and with Chinese leader Xi Jinping later the same day.

North Korea was likely to be one of the main subjects.

MSDF destroyers held joint drills with the Vinson twice last month in the East China Sea, but tensions with nuclear-armed Pyongyang have hit a fever pitch as the isolated country prepares to mark the 85th anniversary of the founding of the Korean People’s Army on Tuesday.

That anniversary comes less than two weeks after the North staged a massive military parade in Pyongyang to celebrate the 105th anniversary of founder Kim Il Sung’s birth. The North has historically marked important anniversaries with provocative events such as missile launches or nuclear tests.

Tetsuo Kotani, a senior fellow at the Japan Institute of International Affairs in Tokyo, said the joint drills were one of the “flexible deterrent options” set in the 2015 U.S.-Japan defense guidelines.

“The combined exercise aims at preventing unintentional escalation of the current crisis by showing and signaling our intention to use force if they further escalate the situation,” Kotani said of North Korea. “This does not aim at stopping the DPRK’s nuclear and missile programs.”

DPRK refers to the North’s formal name, the Democratic People’s Republic of Korea. South Korea is formally known as the Republic of Korea, or ROK.

On Friday, the North blasted the Vinson’s re-deployment — saying the move was equivalent to the U.S. touting pre-emptive operations and strikes on its leadership. It said any such attacks would result in the “sinking of the Japanese archipelago” in response.

In a statement carried by state-run media, a spokesman for the North’s Korean Asia-Pacific Peace Committee said Pyongyang is keeping “all options available,” ranging from “weapons of mass destruction, such as the hydrogen bomb,” to “intercontinental ballistic missiles.”

“We are not surprised the United States boasts of its strength, while picking on weak nations without nuclear weapons … we will respond to all-out war with all-out war,” the statement read. “Those who threaten the central leadership, our life and dignity, must be ready for South Korea to be turned into ashes, the sinking of the Japanese archipelago and for a nuclear hail to rain down on the mainland of the United States.”

The Vinson-led strike group was expected to arrive in the Sea of Japan “within a matter of days,” U.S. Vice President Mike Pence said Saturday.

“Our expectation is that they will be in the Sea of Japan, in position, in a matter of days, before the end of this month,” Pence said during a joint news conference in Sydney with Australian Prime Minister Malcolm Turnbull.

Days earlier, there had been widespread confusion over the whereabouts of the strike group. The navy said it had initially been scheduled to depart Singapore for port calls in Australia, but was rerouted on April 8, reportedly toward waters off the Korean Peninsula as a demonstration of force to the North.

Trump boasted of the strike group in an interview earlier this month with the Fox Business Network, where he described it as “an armada.”

“We are sending an armada. Very powerful,” he said. “We have submarines. Very powerful. Far more powerful than the aircraft carrier. That I can tell you.”

The voyage from Singapore to the Sea of Japan was speculated as taking more than a week.

But photos posted to the U.S. Navy’s website on April 15 showed the carrier transiting the Sunda Strait, the passage between the Indonesian islands of Sumatra and Java — some 5,600 km from South Korea. It was later revealed that the strike group had in fact been completing a training exercise with the Australian Navy.

The White House has denied it offered misleading information on the whereabouts of the Vinson. Pence told the news conference, which was livestreamed, that the decision to dispatch the Vinson to the Korean Peninsula “was set into motion some time ago.”

On Friday, the U.S. Navy revealed the approximate location of the Vinson in a statement announcing that a fighter jet pilot operating from the carrier was forced to eject in the Celebes Sea, south of the Philippines.

Euan Graham, director of the International Security Program at the Lowy Institute in Australia, said the joint U.S.-Japan exercises offered a chance to make up for lost credibility in the wake of the earlier confusion over the Vinson’s location.

“A late-in-the-day chance to redeem some signaling value to Pyongyang from the Vinson’s Korean re-deployment would be good,” he said.