TOKYO (Kyodo) -- Japan said Wednesday it will closely monitor the evolving situation in South Korea to determine its implications on bilateral ties, after the overnight chaos wrought by the temporary but abrupt declaration of martial law.

Prime Minister Shigeru Ishiba, who has pledged to continue improving Japan's ties with South Korea, said the government is watching developments with "particular and grave" concerns.

Asked about his reported interest in visiting South Korea for a summit with President Yoon Suk Yeol in early January, Ishiba told reporters that "nothing specific has been determined."

After Yoon's decision sent shockwaves through democratic South Korea and beyond, a bipartisan group of Japanese lawmakers decided to cancel a mid-December trip by its leader, former Prime Minister Yoshihide Suga, a person familiar with the matter said.

Japan's relations with South Korea, long fraught with difficulties stemming from Japan's wartime aggression and territorial disputes, have thawed since Yoon took office in 2022 as he has sought to improve ties by taking a forward-looking approach.

"We have been monitoring (developments) since the overnight declaration of martial law," Ishiba told reporters, adding that he is not in a position to comment on South Korea's domestic affairs.

"We will do our utmost to ensure the safety of Japanese people in South Korea," he said.

Yoon, recently facing sluggish public approval ratings, abruptly declared martial law late on Tuesday to rein in what he described as "anti-state" activities.

While the declaration was lifted hours later, Yoon's move still drew immediate criticism from lawmakers and locals, who viewed it as anti-democratic and triggered calls for his resignation.

Ishiba, who took over from Fumio Kishida as prime minister in October, has stressed the importance of maintaining momentum toward improved ties between the key U.S. allies in East Asia.

As next year marks the 60th anniversary of the normalization of bilateral ties, Ishiba has been considering making a trip to South Korea in early January to sit down with Yoon, diplomatic sources said earlier.

"Depending on how the situation unfolds, it may impact (the trip plan)," a senior Japanese Foreign Ministry official said.

Three-way cooperation with the United States has become all the more important due to North Korea's nuclear and missile development. Yoon has taken a tougher stance on Pyongyang than his predecessor.

"Defense cooperation with South Korea as well as coordination among Japan, South Korea and the United States are extremely important for our country's security," Defense Minister Gen Nakatani separately told reporters.

Japanese businesses are also keeping close tabs on the situation while gathering updates.

The Asian neighbors have seen an uptick in interactions, with South Korea among popular destinations for Japanese tourists and vice versa.

Japan Airlines Co., which, along with All Nippon Airways Co., operates flights linking the two countries, said it is prepared to "consider necessary measures immediately" however the situation develops.

Fast Retailing Co. said around 130 Uniqlo casual clothing shops it operates in South Korea will remain open as usual.

Japanese officials expressed hope that there will be no further problems in South Korea, with one concerned that the latest developments could upend the recent improvement in ties between the two nations.

"Japan and South Korea have been trying to develop bilateral ties by overcoming difficulties so we hope that the political situation will be calm and stable," a senior government official said.