North Korea fired four missiles into the Sea of Japan on Monday, according to officials in Seoul and Tokyo, in a move likely to escalate tensions that are already running high in the region.

One of the currently unidentified projectiles could be an intercontinental ballistic missile, said a South Korean military official without providing further details. If confirmed, such a launch would mark a new phase in Pyongyang’s programme to develop long-range, nuclear-capable missiles.

In January, Pyongyang announced it was able to launch a long-range missile, capable of hitting the US, whenever it chose. The country has never proven such capabilities, but the remarks elicited a rebuke from President Donald Trump. “North Korea just stated that it is in the final stages of developing a nuclear weapon capable of reaching parts of the US. It won’t happen!” the US president tweeted at the time.