A rare joint exercise of three U.S. aircraft carrier strike groups — a combination wielding massive firepower — will occur in coming days in the Western Pacific as part of a pressure campaign on North Korea by the Trump administration.

A U.S. official Monday confirmed the planned linkup by the USS Ronald Reagan, USS Nimitz and USS Theodore Roosevelt strike groups.

The Pearl Harbor guided-missile destroyers USS Halsey and USS Preble, each with over 330 sailors, pulled into Guam for a port visit with the carrier Theodore Roosevelt on Oct. 31.

The destroyer USS Chafee, also out of Hawaii, is participating in an exercise with South Korean and Australian warships off the coast of South Korea’s Jeju island, meanwhile.

Not since 2007 and the exercise Valiant Shield off Guam have three aircraft carriers operated together in the Pacific, the Navy said. The gathering is seen as a show of force aimed at a belligerent North Korea.

A day after President Donald Trump touched down in Hawaii on Friday on the start of his first Asia trip, a group of 16 members of Congress who are military veterans, including U.S. Rep. Tulsi Gabbard from Hawaii, issued a joint statement cautioning against military action against North Korea.

The mostly Democratic group also said the president “needs to stop making provocative statements that hinder diplomatic options.”

Trump on Monday left Japan for South Korea. In Tokyo at a joint press conference, Japanese Prime Minister Shinzo Abe said there “is no point in the dialogue for the sake of dialogue with North Korea. Now is the time not for dialogue, but for applying maximum pressure on North Korea.”

Abe said Japan and the United States must take a leadership role in collaborating with the international community to enhance that pressure “through all possible means.”

Trump, meanwhile, said North Korea’s unlawful weapons program is a threat to the civilized world. “We will not stand for that. The era of strategic patience is over,” he said.

The Theodore Roosevelt strike group alone has about 7,500 sailors and Marines. About a dozen escort ships, 225 aircraft and submarines are accompanying the three carriers.

The congressional statement noted that a report by the Congressional Research Service said conflict on the Korean Peninsula could affect as many as 25 million people on either side of the border.

The Joint Chiefs of Staff also said the only way to locate and destroy with complete certainty all components of North Korea’s nuclear weapons program is through a ground invasion.

Every diplomatic and economic option must be exhausted before military options are considered, the congressional group said.

The assessments underscore “what we’ve known all along: There are no good military options for North Korea,” the statement said. “Invading North Korea could result in a catastrophic loss of lives for U.S. troops and U.S. civilians in South Korea. It could kill millions of South Koreans and put troops and civilians in Guam and Japan at risk.”