North Korea fires two short-range ballistic missiles into the East Sea on Friday.
South Korea's military spots the launch, the latest in a series of sanctions-busting tests.
This year has seen an unprecedented number of tests by North Korea, including an ICBM and rocket engine.
The US and South Korea warn of a potential seventh nuclear test.
On Tuesday, the two countries hold a joint air drill and deploy a US B-52H bomber to the peninsula.
Friday's missile launch follows news that North Korea delivered arms to the Russian group Wagner.
North Korea denies conducting any arms transactions with Russia.
Despite sanctions, North Korea has developed a range of ICBMs and recently tested a "high-thrust solid-fuel motor."
Kim Jong Un wants North Korea to be the world's most powerful nuclear force.