North Korea has attempted to fire a ballistic missile off its east coast but the launch appears to have failed, South Korean military officials say, according to BBC News.

It is unclear what type of missile it was, but it follows three failed tests of the medium-range "Musudan" missile in April.

The North is banned by the UN from using any ballistic missile technology.

Tensions have run high in the region after Pyongyang's fourth nuclear test in January and numerous missile tests.

Also on Tuesday, May 31, the newly promoted vice-chairman of North Korea's ruling Workers Party, Ri Su-yong, arrived in China for what South Korean media said was an unannounced official visit.

China is North Korea's closest ally and trading partner, but ties have been strained by the nuclear test and weapons activity.

It is the first visit since the Worker's Party congress earlier this month in North Korea, the first in 36 years.

Ri, who was travelling with a large entourage, would likely be briefing China on other major developments at the congress, in an attempt to rebuild the relationship, said Yonhap.