It was the fifth round of test launches in two weeks to protest US-South Korea joint military drills, Seoul says.

North Korea has fired what appeared to be two short-range ballistic missiles into the sea, according to South Korea‘s military, the latest in a series of launches to protest US-South Korea joint military drills.

Defence officials in Seoul said the missiles were fired early on Saturday from near North Korea’s northeastern city of Hamhung, flying 400km at a height of about 48km before splashing down in the sea between the Korean Peninsula and Japan.

“Our military is monitoring the situation in case of additional launches while maintaining a readiness posture,” South Korean military’s joint chiefs of staff said in a statement.

A US official said at least one projectile was launched and that it appeared to be similar to previous short-range missiles fired by Pyongyang.

It was the fifth round of launches in two weeks, with North Korean leader Kim Jong Un labelling them a “solemn warning” over the joint military exercises that began on Monday.

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

North Korea did not immediately comment on the latest launches.

Saturday’s tests came a few hours after US President Donald Trump said he had received a “very beautiful letter” from Kim and reiterated that he wasn’t bothered by the recent flurry of short-range weapons launched.

“I’ll say it again. There have been no nuclear tests. The missile tests have all been short-range. No ballistic missile tests. No long-range missiles,” Trump told reporters on Friday.

Stalled talks

North Korea’s recent tests have dampened the optimism that followed the third and latest meeting between Trump and Kim on June 30 at the inter-Korean border.

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

So far, North Korea has stuck by its unilateral suspension of nuclear and long-range missile tests, which came during its diplomatic outreach to Washington last year.

Kim has said the latest weapons tests were a response to US-South Korean military drills being held this month.

Trump said he agreed with Kim’s opposition to the war games – albeit for financial rather than military reasons.

“He wasn’t happy with the war games. I’ve never liked it either. I’ve never been a fan. And you know why? I don’t like paying for it,” Trump said.

Experts say Trump downplaying North Korea’s launches has allowed the country more room to intensify its testing activity while it seeks to build leverage ahead of negotiations.

“The North is up to humiliate the US president,” said Gordon Chang, author of Nuclear Showdown: North Korea Takes On the World.

“This is the first stage of an escalatory cycle. The North Koreans will continue up that stage, and when they do it will be much more difficult in the later parts of the cycle to stop it and certainly much more dangerous,” he told Al Jazeera.

“Trump needs to change his policies and pose some costs on North Korea for violating these UN Security Council resolutions on missile launches.”

UN resolutions prohibit North Korea from launching ballistic missiles, whether short-, medium- or long-range.