Japan and the United States said Monday they were ready to act again following their first joint action in 28 years to boost the yen, after the beleaguered currency hit a four-decade low.

Coordination between Japan and the United States now appears to be the tightest in decades, fuelling one of the most notable rebounds since the yen began its years-long slide.

The degree of coordination between the two countries now appears to be the tightest in decades, which has raised the stakes for traders betting against the yen.

Japan's Finance Minister plans to reveal a cooperation with Washington regarding currency market interventions aimed at arresting the yen's drastic decline to levels not seen in…