North Korea has fired two suspected short-range missiles from the west of the country, according to South Korea's military.
It is the North's second weapons launch in the last five days and a possible warning that nuclear disarmament talks with Washington could be in danger.
The South's Joint Chiefs of Staff said that the weapons fired flew 260 miles and 167 miles respectively. It said it is working with the US to find out more details, such as the type of weapons the North fired.
The South's military said earlier at least one projectile was launched from the Sino-ri area of North Pyongan Province, an area known to host one of North Korea's oldest missile bases where a brigade operates mid-range Rodong missiles.
It said later the launch was made from the province's Kusong town, about 25 miles from Sino-ri, where the North conducted its first successful flight test of the Hwasong-12 intermediate range missile in May 2017.
The launch comes as the US special representative for North Korea, Stephen Biegun, visits South Korea, and hours after the North described its firing of rocket artillery and an apparent short-range ballistic missile on Saturday as a regular and defensive military exercise.
The North also ridiculed South Korea for criticising those launches.
South Korea's presidential national security director, Chung Eui-yong, has been monitoring the situation while communicating with the defence ministry and the Joint Chiefs of Staff.
Some analysts have said that if the North returns to testing the kind of longer-range banned ballistic weapons that it fired in unusually large numbers in 2017 – when many feared a Washington-Pyongyang stand-off could end in war – it may signal that a frustrated North Korea is turning away from diplomacy.
The tensions in 2017 were followed by a surprising diplomatic outreach by North Korean leader Kim Jong Un in 2018, when he attended summits with the South Korean and Chinese presidents and with US President Donald Trump.
But North Korea has not received what it wants most from the summits: Sanctions relief.
A summit earlier this year between Mr Trump and Mr Kim ended in failure, with the US not believing that North Korea was offering enough disarmament steps to agree to the widespread sanctions relief the North wants.
Just ahead of the Thursday launch, senior defence officials from South Korea, the US and Japan met in Seoul to discuss North Korea's launches on Saturday and other security issues.
Experts who analysed photos from North Korean state media say it is clear the North on Saturday tested a new solid-fuel missile that appears to be modelled after Russia's Iskander short-range ballistic missile system.
With the consecutive weapons launches, North Korea is pressuring South Korea to diverge from the US to support the North's position more strongly, said Du Hyeogn Cha, a visiting scholar at Seoul's Asan Institute for Policy Studies.
Following the collapse of the Trump-Kim meeting, the North had demanded the South proceed with inter-Korean economic projects held back by US-led sanctions against the North.
By firing weapons that directly threaten the South but not the US mainland or its Pacific territories, the North also appears to be testing how far Washington would tolerate its actions without actually causing the negotiations to collapse, Mr Cha said.
"To the United States, the North is saying 'don't push me into a corner'. To South Korea, the North is saying the inter-Korean peace agreements could become nothing if Seoul fails to coax major concessions from the United States on behalf of the North," he said.
South Korean and US officials have described what North Korea fired on Saturday as "projectiles", a broader term that include both missiles and artillery pieces. This could be an effort to keep diplomacy alive as UN sanctions bar the North from engaging in any ballistic activity.
Some observers say the North could fire more missiles, including those of a medium range, to up the pressure on the US.
Mr Cha said North Korea is unlikely to fire longer-range missiles unless it intends to abandon diplomacy for good as it is certain to invite fresh UN sanctions.
North Korea last conducted a major missile test in November 2017.
Mr Kim, in a new year's speech, said he hopes to continue his nuclear summits with Mr Trump, but also that he would seek a "new way" if the US persists with sanctions and pressure against the North.
Following the collapse of his second summit with Mr Trump in February, Mr Kim said he is open to a third meeting, but set the year's end as a deadline for Washington to offer mutually acceptable terms for an agreement.