North Korea fired an apparent intermediate-range missile off its east coast on Sunday, South Korea said, as tensions run high after Pyongyang's recent launches of an intercontinental ballistic missile and its first military spy satellite.

A projectile believed to be the missile has fallen, according to the Japanese coast guard, which said it could be a ballistic missile. It appeared to have fallen outside Japan's exclusive economic zone, public broadcaster NHK said.

In November, North Korea said it successfully tested new solid-fuel engines designed for intermediate-range ballistic missiles.

Sunday's missile was fired from the area of Pyongyang around 2:55 p.m. (0555 GMT), South Korea's military said in a statement, adding that Seoul was is running an analysis on the missile in coordination with the United States and Japan.

North Korea has been stepping up pressure on Seoul in recent weeks, declaring it the "principal enemy", saying the North will never reunite with the South and vowing to enhance its ability to deliver a nuclear strike on the U.S. and America's allies in the Pacific.

In December, North Korea said it had tested its newest intercontinental ballistic missile to gauge the war readiness of its nuclear force against what it called mounting U.S. hostility, as Washington and its allies began operating a real-time missile data sharing system.

North Korean soldiers brought heavy weapons back to the Demilitarized Zone around the North-South border and restored guard posts that the two countries had demolished, after Seoul suspended part of a 2018 military accord between the two Koreas in a protest over Pyongyang's launch of the spy satellite.

Pyongyang's isolated government is forging closer ties with Moscow. Foreign Minister Choe Son Hui will visit Russia from Monday to Wednesday at the invitation of her counterpart Sergei Lavrov, KCNA news agency said on Sunday.

The United States and its allies have condemned what they described as Russia's firing of North Korean missiles at Ukraine, with Washington calling it abhorrent and Seoul calling Ukraine a test site for Pyongyang's nuclear-capable missiles.

Moscow and Pyongyang have denied conducting any arms deals but vowed last year to deepen military relations.

The U.S. State Department on Thursday imposed sanctions on three Russian entities and one individual involved in the transfer and testing of North Korea's ballistic missiles for Russia's use against Ukraine.