According to South Korea’s military, North Korea has conducted another missile test on May 21.
Meanwhile, the White House said the medium-range missile had a shorter range than those used in North Korea’s last three tests.
The move comes a week after North Korea tested what it said was a new type of rocket capable of carrying a large nuclear warhead.
On May 15, the UN Security Council again demanded that North Korea conduct no further such tests.
The UN Security Council is now scheduled to meet behind closed doors on May 23 – a meeting requested by the US, South Korea and Japan.
South Korea’s foreign ministry earlier said the launch was “reckless and irresponsible”, while Secretary of State Rex Tillerson described it as “disappointing” and “disturbing”.
The latest missile flew about 350 miles towards the Sea of Japan, South Korea’s Joint Chiefs of Staff said. Last week’s missile travelled about 435 miles.
Japanese news agencies said the missile probably fell into the sea outside Japan’s waters.
Japan’s Chief Cabinet Secretary Yoshihide Suga told a news conference a protest had been lodged with North Korea.
North Korea is known to be developing both nuclear weapons – it has conducted five nuclear tests – and the missiles capable of delivering those weapons to their target. Both are in defiance of UN sanctions.
South Korea said the latest test was conducted in Pukchang, in the west of the country. A missile exploded soon after take-off from Pukchang last month.
Earlier on May 21, North Korea’s state-run media had said it would continue to launch more “weapons capable of striking” the US.
In early May, the US said a missile defense system it had installed in South Korea was now operational.
The THAAD system can intercept North Korean missiles, although full operational capability is still some months away. North Korea and its ally China have condemned the installation of the system.
However, there is no sign that THAAD was used against the missile tested on May 21.
Newly-installed South Korean President Moon Jae-in, who is seeking deeper engagement with North Korea, has convened an urgent meeting of his national security council in response.