After talks with U.S. Secretary of State John Kerry in the U.S. capital Friday, Japan's top diplomat emphasized the importance of mending ties between Seoul and Tokyo.

"There are difficult issues in the relationship between Japan and the Republic of Korea, but Republic of Korea is an important neighbor for Japan," Foreign Minister Fumio Kishida told reporters, with Kerry standing next to him.

He added the Japanese government will make "tenacious efforts" for a cooperative relationship with South Korea "from a broad perspective."

The minister said he and Kerry agreed that trilateral cooperation with South Korea should continue to achieve denuclearization of Korea.

Amid strained ties between South Korea and Japan over territorial claims and their shared history, the U.S. has suffered a setback in its push for a stronger tripartite partnership in handling regional security challenges.

When Japan's conservative prime minister, Shinzo Abe, paid homage at a controversial Tokyo war shrine in December, the U.S. expressed disappointment.

But Kerry did not make any direct mention of the Seoul-Tokyo feud during the joint press availability without a question-and-answer session.

The secretary focused more on Japan's stand-off with China.

The U.S. remains committed to upholding its defense treaty obligations with Japan in regard to Tokyo's territorial disputes with Beijing in the East China Sea, he said.

And the U.S. will never recognize China's unilateral declaration of its own air defense identification zone in the area, added Kerry.

"The United States has no intention of changing how we conduct operations in the region," he said.

Kishida said that Washington and Tokyo agreed to respond "calmly and with resolve" to China's aggressive move.

On President Barack Obama's upcoming trip to Asia, Kishida formally invited him to visit Japan.

Obama plans to visit Asia in April, but the White House has not announced his itinerary.

Many expect the president to visit Japan, and keen attention is being paid to how long he will stay there.

Should he make a state visit to Tokyo, which will likely last two to three days, chances that he will not travel to South Korea this time around would grow because of his tight schedule, according to diplomatic sources.

"When the United States makes its decision, the Japanese side will cooperate so that we will be able to make sure that President Obama's visit to Japan is a great success," Kishida said.

Kerry, meanwhile, is scheduled to visit Seoul for two days toward the end of next week, according to a government source in Seoul.

During his stay, the secretary is expected to hold talks with his South Korean counterpart Yun Byung-se and pay a courtesy call on President Park Geun-hye, the source said, requesting anonymity.

The two sides are likely to discuss the security situation on the Korean Peninsula, including ways to deter North Korean provocations and revive the stalled six-party talks on getting the communist state to abandon its nuclear weapons program, officials said.

South Korea's request for a visit to Seoul by Obama in April will also likely be discussed, they added.

The last time Kerry visited South Korea was in April. (Yonhap)