By Josh Smith

SEOUL (Reuters) -South Korean President Yoon Suk Yeol, who vowed to make his country a "global pivotal state", faced immediate international diplomatic fallout on Wednesday after his botched attempt to impose martial law.

Yoon declared martial law in a live TV address late on Tuesday night, only to reverse course six hours later after parliament defied police and special forces cordons to vote to block the move.

Swedish Prime Minister Ulf Kristersson, who was due to hold a summit with Yoon this week, will skip the scheduled visit, his spokesperson said on Wednesday.

"Given the recent developments, we have decided to postpone the visit," the spokesperson said in a statement.

The United States, South Korea's main ally, indefinitely postponed meetings of the Nuclear Consultative Group and related tabletop military exercises, a U.S. official said, speaking on condition of anonymity.

The NCG is a signature Yoon effort aimed at having South Korea play a greater role in allied planning for potential nuclear war on the peninsula.

Around 28,500 U.S. troops are stationed in South Korea and it was not immediately clear if other joint military exercises would be affected. A spokesperson for U.S. Forces-Korea did not respond to a request for comment.

The U.S. and South Korean militaries are "in contact", the Pentagon said on Tuesday, adding there was no request for assistance from Seoul amid the unfolding events.

Pentagon spokesperson Major General Patrick Ryder told a news briefing he also did not believe the martial law declaration had any significant impact so far on the U.S. troops, some of whom work in combined commands with the South Korean military.

A White House spokesperson earlier said the U.S. was not notified in advance of Yoon's announcement and added: "We are seriously concerned by the developments we are seeing on the ground."

The martial law declaration cast doubts over a possible visit next week by U.S. Defense Secretary Lloyd Austin. Japanese media reported he was due to meet South Korean and Japanese counterparts as part of trilateral efforts championed by Yoon.

Japan's lawmaker group on Korean affairs led by former premier Yoshihide Suga cancelled a Seoul visit slated for mid-December, according to Akihisa Nagashima, a special advisor to Japan's prime minister who was due to travel with the group.

"The turmoil in South Korea's domestic politics since last night continues to be alarming," Nagashima wrote in a post on X.

"It is a tense situation in which the fate of the Yoon administration must be closely watched to see whether it will be able to overcome the fierce public opposition."

Japanese Prime Minister Shigeru Ishiba earlier told reporters Tokyo was monitoring the situation "with particular and grave interest."

Duyeon Kim of the Center for a New American Security said Yoon’s international reputation as a symbol of democracy had been ruined.

"The fate of Yoon’s foreign policies remains uncertain and even bleak," she added.

(Reporting by Josh Smith; Additional reporting by Idrees Ali in Washington, and John Geddie and Kantaro Komiya in Tokyo; Editing by Stephen Coates and Lincoln Feast.)