North Korea launched a "newly developed, new-type tactical-guided projectile" on Thursday, state news agency KCNA reported on Friday.
The US condemned the launches and spoke of a threat to international peace and security.
The launches, the country's first ballistic missile tests in about a year, underscored steady progress in its weapons programme amid stalled denuclearisation talks with the US.
President Joe Biden said on Thursday the US was open to diplomacy with North Korea despite its missile tests this week, but said there would be responses if North Korea escalates matters.
The State Department later condemned the ballistic missile launches as destabilising. "These launches violate multiple UN Security Council resolutions and threaten the region and the broader international community," a State Department spokesman said.
The new weapon is based on existing technology that was improved to carry a 2.5-tonne warhead, KCNA reported.
KCNA said the two weapons struck a target 600 kilometres off North Korea's east coast, which conflicts with estimates by South Korean and Japanese authorities who said the missiles flew about 420-450km.
"The development of this weapon system is of great significance in bolstering the military power of the country and deterring all sorts of military threats," said Ri Pyong-chol, the senior leader who oversaw the test, KCNA reported.
Photos released by state media show a black-and-white-painted missile blasting off from a military launch vehicle.
Missile specialists at the California-based James Martin Centre for Nonproliferation Studies said it appeared to be a missile that was unveiled at a major military parade in Pyongyang in October.
If it is, then Thursday's missiles were probably an improved and stretched variant of the previously tested KN-23 missile with "a really big warhead," the centre's Jeffrey Lewis said.
The KN-23 is a North Korean short-range ballistic missile (SRBM) first tested in May 2019, visually similar to Russia's Iskander-M SRBM, prompting analysts to debate whether it was developed with foreign help.
The new missile's 2.5-tonne warhead may be a response to South Korea's announcement in August that its latest Hyunmoo-4 SRBM had "the largest payload in the world" at two tonnes, Mr Lewis said.
The SRBMs developed by North Korea are designed to defeat missile defences and conduct a precision strike in South Korea, analysts say.
KCNA said Thursday's test confirmed the missile's capability to conduct "low-altitude gliding leap-type flight mode", a feature that makes such weapons harder to detect and shoot down.
KCNA's report suggested North Korean leader Kim Jong-un did not attend the launch, and undated state media photos published on Friday showed him inspecting new passenger buses in Pyongyang.
Mr Kim has vowed to improve living conditions for citizens as North Korea's economy is ravaged by numerous crises, including international sanctions over the missile and nuclear weapons programmes, natural disasters and a crushing self-imposed border lockdown – an effort to prevent a coronavirus outbreak – that slowed trade to a trickle.
