North Korea fired two short-range ballistic missiles early this morning, the South Korean military said, only days after it launched two similar missiles intended to pressure South Korea and the United States to stop upcoming military drills.

It follows launches on 25 July, which were North Korea's first missile tests since leader Kim Jong-un and US President Donald Trump met on 30 June and agreed to revive stalled denuclearisation talks.

The series of missile tests raises the stakes for US and South Korean diplomats criss-crossing the region this week in the hope of restarting talks aimed at persuading Pyongyang to give up its nuclear weapons and ballistic missile programmes.

"North Korea's actions do not help ease military tensions, nor do they help keep the momentum for talks that are under way," South Korean Foreign Minister Kang Kyung-wha told reporters in Seoul before leaving for a Southeast Asian security forum in Bangkok.

He urged North Korea to stop the missile launches.

US Secretary of State Mike Pompeo and the top US North Korea negotiator were also headed to the Association of Southeast Asian Nations (ASEAN) Regional Forum in the Thai capital, where Mr Pompeo said he was holding out hope that US officials could meet North Korean counterparts.

Mr Trump and Mr Pompeo both played down last week's launches and Mr Pompeo has continued to express hope for a diplomatic way forward with North Korea.

The latest launch comes ahead of newly appointed US Secretary of Defense Mark Esper's first official visit to Seoul, which the Pentagon said yesterday was scheduled as part of a tour through Asia in August.

US military forces in South Korea were aware of today's launch, a spokesman said.

The launches were from the Wonsan area on North Korea's east coast, the same area from where missiles were fired last week, South Korea's Joint Chiefs of Staff (JCS) said in a statement.

It said it was monitoring in case of more launches.

The JCS said later the North had fired ballistic missiles that flew about 250km and that they appeared to be similar to those launched last week.

The missiles, dubbed the KN-23, are designed to evade missile defence systems by being easier to hide, launch, and manoeuvre in flight, experts said.