North Korea's leader Kim Jong-un has announced Pyongyang will carry out no more ballistic missile tests and will shut down its nuclear test site, the latest olive branch from the regime as diplomacy in the region ramps up.

The declaration, long sought by the US, was welcomed by foreign powers including the UK, but analysts cautioned that the pledges also raised a number of questions.

The diplomatic gesture from North Korea comes less than a week before Mr Kim meets South Korean leader Moon Jae-in for a summit, and ahead of a much-anticipated encounter with US President Donald Trump.

"As the weaponisation of nuclear weapons has been verified, it is not necessary for us to conduct any more nuclear tests or test launches of mid- and long range missiles or ICBMs," Mr Kim told a ruling party meeting.

"The northern nuclear test site has completed its mission," he added at the gathering of the central committee of the Workers' Party, according to the official KCNA news agency.

Mr Trump welcomed the announcement and said he was looking forward to the summit.