North Korea has fired what appeared to be two short-range ballistic missiles into the sea, according to South Korea’s military.

The launches are the fifth round in less than three weeks in what is being seen as a protest at the slow pace of nuclear negotiations with the United States and the continuance of US-South Korea joint military exercises.

South Korea’s military alerted reporters to the launches hours after US President Donald Trump said he had received a “beautiful” three-page letter from North Korean leader Kim Jong Un and predicted that they will have more talks to try resolving the nuclear standoff.

People watch a TV news programme reporting about North Korea’s projectiles Credit: Lee Jin-man/AP

Mr Trump reiterated that he was not concerned by the flurry of short-range weapons Mr Kim has launched despite the growing threat they pose to US allies in the region.

South Korea’s Joint Chiefs of Staff said the presumed ballistic missiles were fired from the North’s eastern coast and flew about 250 miles before landing in waters between the Korean peninsula and Japan.

Seoul’s presidential office said the tests were probably aimed at verifying the reliability of the North’s newly developed weapons and demonstrating displeasure over the allied drills.

The North has unleashed a series of test firings of short-range weapons in recent weeks while saying the joint military drills between the allies compel it to “develop, test and deploy the powerful physical means essential for national defence”.

Experts say Mr Trump’s downplaying of the North’s launches allowed the country more room to intensify its testing activity while it seeks to build leverage ahead of negotiations, which could resume some time after the end of the allies’ drills later this month.

The allies have scaled down their major military exercises since the first summit between Mr Kim and Mr Trump in June 2018 in Singapore created space for diplomacy.

North Korean leader Kim Jong Un visits an airfield in the western area of North Korea to watch its weapons demonstrations. Credit: KNCA/AP

But the North insists even the downsized drills violate agreements between the pair.

The North’s recent tests have dampened the optimism that followed the third and latest meeting between the leaders of the US and North Korea on June 30 at the Korean border.

They agreed to resume working-level nuclear talks, but there have been no known meetings between the two sides since then.