North Korea fired two unidentified projectiles into the sea off its east coast on Tuesday, the South Korean military said, as Pyongyang's foreign ministry protested that joint US-South Korea military drills violated diplomatic agreements.
The North, criticising the US-South Korean drills and their use of high-tech weapons, has fired a series of missiles and rockets since its leader Kim Jong Un and US President Donald Trump agreed at a June 30 meeting to revive stalled denuclearisation talks.
Trump has played down the tests by saying they did not break any agreement he had with Kim but the talks have yet to resume. Analysts believe the tests are designed both to improve North Korean military capabilities and to pressure Washington to offer more concessions.
A senior Trump administration official said: "We continue to monitor the situation and are consulting closely with our South Korean and Japanese allies."
In Seoul, South Korea's defence minister and the heads of the National Security Office and the National Intelligence Agency were meeting to discuss North Korea's firing of short-range projectiles, said Ko Min-jung, a spokeswoman for the presidential office.
South Korea's Joint Chiefs of Staff (JCS) said the latest projectiles, the fourth set of launches since July 25, were fired from South Hwanghae province early on Tuesday.
The Yonhap news agency in South Korea said the projectiles flew 450 km (280 miles) and reached an altitude of 37 km (23 miles).
The July 25 launches were the first since Trump and Kim met at the heavily armed Demilitarized Zone that separates the two Koreas on June 30.
A North Korean foreign ministry spokesman said in a statement released through state news agency KCNA that North Korea remains committed to resolving issues through dialogue.
However, Pyongyang "will be compelled to seek a new road as we have already indicated" if South Korea and the United States continue with hostile military moves, he said.
The arrival of new, US-made F-35A stealth fighters in South Korea, the visit of a US nuclear-powered submarine to a South Korean port, and US tests of ballistic missiles are among the steps that have forced North Korea to continue its own weapons development, the spokesman said.
"The US and South Korean authorities remain outwardly talkative about dialogue," he said. "But when they sit back, they sharpen a sword to do us harm."
North Korea has repeatedly complained that the United States and South Korea's joint military drills violate a pledge made by Trump to Kim.
South Korean media reported that US-South Korea joint military exercises had started on Monday. A senior South Korean official said previously the drills would mainly involve computer simulations.
A JCS spokesman told a regular news briefing on Monday the allies were preparing for a joint exercise in the second half of the year but would not confirm the name of the exercise or whether it had already started.
A United Nations report said on Monday Pyongyang has "continued to enhance its nuclear and missile programmes" and used cyberattacks to take in $2 billion to fund the development.
The testing of short-range missiles by North Korea is covered by a 2006 United Nations Security Council resolution demanding that North Korea suspend all activities related to its ballistic missile programme.
Short-range missiles pose no threat to US territory but do put at risk US allies Japan and South Korea and the tens of thousands of US troops stationed in both countries.
Japan's defence ministry said it did not see any imminent threat to Japanese security from the latest projectile launch by North Korea.