Japanese government leaders and U.S. Defense Secretary Jim Mattis agreed Friday to work together to achieve North Korea's denuclearization and beef up their alliance deterrence as diplomatic efforts continue to advance nuclear negotiations.

During a series of talks with Japanese Prime Minister Shinzo Abe and other ministers in Tokyo, Mattis offered various reassurances to Japan, including the oft-repeated defense pledge to the key Asia ally, after a suspension of U.S.-South Korea military drills sparked concern about the U.S. commitment to the region.

"We are in the midst of very unprecedented negotiations right now with North Korea. But in this dynamic time...there is absolute reassurance between the two of us that we stand firm," Mattis said at a press conference, shrugging off speculation that Japan-U.S. alliance may be adversely affected by the nuclear talks.

In a sign of the close ties between Washington and Tokyo, Mattis said he "recognizes" the issue of past abductions of Japanese nationals by North Korean agents, a matter of top priority to Japan and an emotional topic.

Abe and Mattis agreed that the two countries will step up cooperation to resolve the abduction issue, such as by sharing information with the U.S. Defense Department that is working on issues related to prisoners of wars and people who went missing in the 1950-53 Korean War.

Mattis was offered a blue ribbon lapel pin, an emblem of the campaign to seek the return of the abductees, and wore it, Japanese Defense Minister Itsunori Onodera told reporters after holding talks with Mattis.

Mattis visited Japan for the first time following the historic summit between U.S. President Donald Trump and North Korean leader Kim Jong Un in Singapore on June 12, at which Kim pledged to work toward the "complete denuclearization" of the Korean Peninsula.

While North Korea's denuclearization commitment was welcome news to Japan, Trump surprised U.S. allies with his abrupt announcement that the United States would be "stopping the war games" with South Korea as long as dialogue continues with Pyongyang.

The remarks have been seen as a major concession to North Korea that has long denounced U.S.-South Korea military drills as rehearsals for an invasion. Pyongyang has also linked its pursuit of nuclear weapons to what it calls "hostile" U.S. policy, including the deployment of 28,500 American troops in South Korea.

(Itsunori Onodera, center left, and Jim Mattis in Tokyo)

Mattis said at the press conference Friday that the pause in U.S.-South Korea military exercises was a decision taken to create "space for our diplomats to negotiate strongly and increasing the prospect for a peaceful solution on the (Korean) Peninsula."

So far, the U.S. Defense Department has announced the suspension of a major annual military exercise slated for August, called Ulchi Freedom Guardian, and two more drills that had been planned in the next three months.

Tokyo has grown concerned that the halt of the exercises may be a sign the United States is pulling away from its commitment to Northeast Asia, with Trump having expressed hope of eventually reducing or withdrawing the U.S. troops in South Korea.

Mattis explained to Onodera that the United States is not considering withdrawal or drawdown of the U.S. military presence in South Korea, according to the Japanese Defense Ministry.

The two also agreed that the military drills between the United States and South Korea, as well as trilateral exercises involving the two countries and Japan, are "important for the stability of the region."

"We agreed that we will reinforce our alliance's deterrence force and response capabilities, such as by steadily carrying out Japan-U.S. joint exercises," Onodera said at a press conference.

Regarding Tokyo's concern at the threat posed by North Korea's shorter-range missiles, Mattis agreed with Onodera that their goal is to make North Korea abandon all weapons of mass destruction, as well as ballistic missiles of all ranges in a complete, verifiable and irreversible manner, Onodera said.

Mattis reaffirmed that the United States is committed to the defense of Japan and that the commitment extends to the Japanese-controlled Senkaku Islands in the East China Sea, which China claims and calls Diaoyu, according to Onodera.

Mattis is on the final leg of a weeklong trip to Asia that has also taken him to China and South Korea.

In South Korea, Mattis reassured his counterpart Song Young Moo that the United States will maintain its current troop levels in South Korea and that the U.S. defense commitment to its key Asian ally remains "ironclad."