"North Korea fired unidentified projectiles eastward" from Sino-ri in North Pyongan province, the South's Joint Chiefs of Staff said in a statement.

The launch came just days after North Korea carried out a military drill and fired multiple projectiles, with at least one believed to be a short-range missile.

It was also hours after the US Special Representative on North Korea, Stephen Biegun, arrived in Seoul late Wednesday for talks with South Korean officials on the allies' approach towards Pyongyang.

It is Biegun's first visit to Seoul since the Hanoi summit between US President Donald Trump and the North's leader Kim Jong Un collapsed without agreement.

"We are still analysing whether it is a single or multiple projectiles," JCS spokesman Kim Joon-rak told AFP.

Pyongyang, Seoul and Washington have refrained from calling Saturday's launch a missile, which could jeopardise the ongoing diplomacy by violating UN Security Council resolutions as well as Kim's promise of a freeze on long-range missile tests.

The North has said Saturday's drill involved multiple Pyongyang "long-range multiple rocket launchers and tactical guided weapons".

But experts say the North launched at least one short-range missile during the exercise, with a report on the respected 38 North website suggesting that it was a "direct import" of a Russian-produced Iskander.

"The debris generated by the launch in North Korea is a virtual match of a launch of Iskander conducted by Russia," it said.

If North Korea imported Iskanders from Russia, the report added, "it has an existing capacity to deliver warheads to targets in South Korea with great precision".

A summit between South Korean President Moon Jae-in and the North's Kim Jong Un a year ago triggered a rapid diplomatic thaw on the peninsula, paving the way for a historic first meeting between Kim and Trump.

But their second summit in Hanoi in February broke up without agreement on sanctions relief and what Pyongyang might offer in exchange, and the North has since blamed Seoul for siding with Washington, leaving inter-Korean relations in limbo.

A spokesman for the North's delegation for military talks with the South said earlier Thursday that Saturday's "routine drill" was conducted within its own waters and added the "flying objects" did not pose any threat to the US, South Korea and Japan.

"The firing of the intermediate- and long-range missile and the ICBM was not involved in it," he said in a statement carried by the official Korean Central News Agency.