SEOUL • North Korea fired what appeared to be two short-range ballistic missiles into the ocean off its east coast yesterday, the latest in an unprecedented flurry of launches that South Korea decried as "inappropriate" amid the global coronavirus pandemic.

Two "short-range projectiles" were launched from the coastal Wonsan area, flew 230km and reached a maximum altitude of 30km, South Korea's Joint Chiefs of Staff (JCS) reported.

"In a situation where the entire world is experiencing difficulties due to Covid-19, this kind of military act by North Korea is very inappropriate and we call for an immediate halt," JCS said in a statement, according to Yonhap news agency.

Japan's Ministry of Defence said they appeared to be ballistic missiles, and they did not land in Japanese territory or its exclusive economic zone.

They would be the eighth and ninth missiles launched in four rounds of tests this month, as North Korean troops conduct ongoing military drills, usually personally overseen by leader Kim Jong Un.

That would be the most missiles ever fired in a single month by North Korea, according to a tally by Mr Shea Cotton, a senior researcher at the James Martin Centre for Nonproliferation Studies.

"Coming this early in the year, the only time we've seen tests this frequently were in 2016 and 2017, both of which were huge years for North Korea's missile programme," he said in a post on Twitter.

All of the missiles fired so far this year have been small, short-range weapons, such as the KN-24 fired during the last launch on March 21.

A day later, North Korean state media said United States President Donald Trump had sent a letter to Mr Kim detailing a plan to develop ties.

The report cited Mr Kim's powerful sister Kim Yo Jong, who warned that the apparently good personal relationship between the two leaders would not be enough to kick-start broader relations.

"In the letter, he... explained his plan to propel the relations between the two countries of the Democratic People's Republic of Korea (DPRK) and the US and expressed his intent to render cooperation in the anti-epidemic work," she said in the statement reported by the North's Korean Central News Agency.

A senior US administration official confirmed Mr Trump had sent a letter to Mr Kim, "consistent with his efforts to engage global leaders during the ongoing pandemic".

Mr Kim has warned that North Korea is developing a new "strategic weapon" to be unveiled this year, with analysts speculating that it could be a new long-range ballistic missile, or a submarine capable of launching such missiles.

United Nations Security Council resolutions bar North Korea from testing ballistic missiles, and the country has been heavily sanctioned over its missile and nuclear weapons programmes.

This month's military drills have been conducted despite a border lockdown and quarantine measures imposed in North Korea in an effort to prevent an outbreak of the coronavirus. The politically and economically isolated country has not reported any confirmed cases, though foreign experts have expressed doubts.

South Korea and the US have postponed some of their joint military exercises due to the outbreak.

North Korea has typically conducted military drills and missile tests in March. For the previous two years, however, it had avoided such springtime launches amid denuclearisation talks with the US.

Those talks have since stalled, and this year's string of tests and military drills appear aimed at underscoring North Korea's return to a more hard-line policy, said Mr Ankit Panda, a senior fellow at the Washington-based Federation of American Scientists.

"There is an element of projecting a business-as-usual image amid the Covid-19 situation, but I think it's not overriding," he said. "These tests do allow Mr Kim Jong Un to show that he's sticking to the hard-line policy he laid out in December last year."

REUTERS