SEOUL — North Korea test-fired two new short-range missiles on Thursday, South Korean officials said, the first such launch since leader North Korean leader Kim Jong Un and US President Donald Trump agreed to revive stalled denuclearization talks last month.

South Korea's Defense Ministry urged the North to stop acts that are unhelpful to easing tension, saying the tests posed a military threat.

It was not immediately clear if the missiles used ballistic technology which would be a breach of UN Security Council resolutions targeting North Korea's missile and nuclear weapons programs.

North Korea launched the missiles from the east coast city of Wonsan with one flying about 430 km (267 miles) and the other 690 km (428 miles) over the sea. They both reached an altitude of 50 km (30 miles), an official at South Korea's Defense Ministry said.

Some analysts said the North appears to have retested missiles it fired in May, but two South Korean military officials said the missiles appeared to be a new design.

The launch casts new doubt on efforts to restart denuclearization talks after Trump and Kim met at the demilitarized zone (DMZ) between the two Koreas at the end of June.

US Secretary of State Mike Pompeo and North Korean Foreign Minister Ri Yong Ho had been expected to meet on the sidelines of a Southeast Asian security forum in Bangkok next week.

But a diplomatic source told Reuters on Thursday that Ri had cancelled his trip.

The White House, Pentagon and US State Department did not immediately respond to requests for comment.

South Korea had detected signs prior to the launch and was conducting detailed analysis with the United States, the presidential Blue House said in a statement.

Japanese Prime Minister Shinzo Abe said the test had no immediate impact on Japan's security, according to Kyodo News.

US National Security Adviser John Bolton, who has taken a hard line towards North Korea, made no mention of the launches in a tweet on Thursday after a visit to South Korea. He said he had "productive meetings" on regional security.

South Korea's nuclear envoy, Lee Do-hoon, had phone calls with his US counterpart, Stephen Biegun, and his Japanese counterpart, Kenji Kanasugi, to share their assessment, South Korea's Foreign Ministry said in a statement.

Chinese Foreign Ministry spokeswoman Hua Chunying told a briefing that Beijing had noted the launch, calling for North Korea and the United States to reopen negotiations "as early as possible".

After Trump and Kim met last month, the United States and North Korea vowed to hold a new round of working-level talks soon, but Pyongyang has since sharply criticized upcoming joint military drills by US and South Korean troops.

North Korea's Foreign Ministry accused Washington this month of breaking a promise by holding military exercises with South Korea. On Tuesday, Kim inspected a large, newly built submarine from which ballistic missiles could be launched.

"By firing missiles, taking issue with military drills and showing a new submarine, the North is sending one clear message: there might be no working-level talks if the United States doesn't present a more flexible stance," said Kim Hong-kyun, a former South Korean nuclear envoy.

Kim Dong-yup, a former navy officer who now teaches at Kyungnam University in Seoul, said the weapons tested on Thursday appeared to be the same as the ones tested in May, which were less of a challenge than long-range missiles but "enough to subtly pressure" Washington.

But the South Korean military believes they may be new, because they traveled further. In May, the projectiles flew only 420 km (260 miles) and 270 km (168 miles) though they reached the same altitude of about 50 km (30 miles).

"We're very cautious because it's difficult to extend the range within such a short time," said one military official, who asked not to be named due to the sensitivity of the issue.

Nuclear talks between North Korea and the United States stalled after a second summit between Trump and Kim in Vietnam in February broke down.

Trump has repeatedly lauded the North's freeze in weapons testing as he is keen for a big foreign policy win as he campaigns for re-election in 2020. — Reuters