US Secretary of State Antony Blinken insisted during a visit to Tokyo on Tuesday that ties with Japan were stronger than ever, days after President Joe Biden blocked Nippon Steel's takeover of US Steel.

Business groups say the decision could have a chilling effect on Japan's standing as the biggest foreign investor in the United States.

With two weeks left before president-elect Donald Trump takes over and Blinken is slated to be replaced by Marco Rubio, the top US diplomat noted that he also came to Japan on his first trip in 2021.

The visits show "not just the importance, the centrality, the United States attaches to our alliance", Blinken said as he met Foreign Minister Takeshi Iwaya.

"This allyship, I believe, it's actually stronger than it's ever been," Blinken said.

Pointing to the need to coordinate after North Korea's launch of a missile Monday -- while he was in South Korea -- Blinken said: "Even though we're in a political transition, the world doesn't stop."

Blinken also cited the strength of economic ties but made no direct mention of Biden's decision last week to block Nippon Steel's US$14.9-billion takeover of long-struggling US Steel, citing national security concerns.

In response, the two companies filed a lawsuit on Monday against the Biden administration's "illegal interference" in the transaction.

"We're certain the lawsuit will reveal a set of facts that clearly violate the constitution and the law, so I believe we have a chance of winning," Nippon Steel chair Eiji Hashimoto said on Tuesday.

Trump, who takes office on January 20, "wants to make manufacturing strong again, and once again enrich the lives and future of manufacturing workers", Hashimoto added.

"This is exactly in line with what we're doing."

Nippon Steel had touted the takeover as a lifeline for a US company long past its heyday but opponents warned the Japanese owners would slash jobs.

Biden had criticised the deal for months, while holding off on a move that could hurt ties with Tokyo.

Japan and the United States are each other's top foreign investors, with Japanese firms investing almost US$800 billion in the United States in 2023. (AFP)