It was nuclear-armed North Korea's first launch since his inauguration -- Pyongyang has been biding its time since the new administration took office, not even officially acknowledging its existence until last week.

Washington is reviewing its approach to Pyongyang after a tumultuous relationship between president Donald Trump and North Korean leader Kim Jong Un, which went from trading insults and threats of war to a diplomatic bromance and several meetings, but made no substantive progress towards denuclearization.

North Korea on Sunday fired two short-range, non-ballistic missiles, US administration officials said Tuesday, but downplayed them as "common" military testing and said they did not violate UN Security Council resolutions.

South Korea's joint chiefs of staff said they appeared to be cruise missiles and were fired over the Yellow Sea, known as the West Sea in Korea -- so towards China, rather than US ally Japan.

The launches followed joint exercises by the US and South Korean militaries earlier this month and came just days after US Secretary of State Antony Blinken and Defense Secretary Lloyd Austin visited Tokyo and Seoul to discuss alliance and security issues in the region, with the North seen as a central threat.

But it was an unusually restrained response by Pyongyang, which has so far not announced them in state media.

Asked by reporters about the tests, Biden said: "According to the Defense department, it's business as usual. There's no new wrinkle in what they did."

A senior US administration official told reporters the launches were "on the low end" of the spectrum of North Korean actions, and nothing like the nuclear weapon tests or intercontinental ballistic missile launches with which Pyongyang has previously provoked Washington.

"It is common practice for North Korea to test various systems," an official added. "We do not respond to every kind of test."

- Reigniting talks -

While Blinken and Austin were in Seoul on March 18, North Korean first vice foreign minister Choe Son Hui accused the United States of a "lunatic theory of 'threat from North Korea' and groundless rhetoric about 'complete denuclearization.'"

President Joe Biden's two-month-old administration hopes to reignite negotiations with the Kim regime on its nuclear arsenal after Trump's headline-grabbing efforts stalled.

Initial outreach from Washington to Pyongyang has turned up empty, but US officials are hopeful they can reconnect, while working in coordination with allies Japan and South Korea.

Trump held two summits with Kim, in Singapore and Vietnam, and the United States pulled back on some joint training activities with South Korea's military while North Korea froze ballistic missile tests.

But their February 2019 meeting in Hanoi broke up over sanctions relief and what the North would be willing to give up in return. Communications then dried up, despite a third encounter in the Demilitarized Zone that divides the Korean peninsula.

Biden officials are now finalizing a strategy to restart talks that the White House will discuss with Japanese and South Korean security officials next week, an administration official said.

"We have taken efforts and we will continue to take efforts" to communicate, they added.

But they said that Pyongyang cannot expect concessions -- such as cutting back on bilateral military exercises -- from Biden.

"Some of the efforts that were taken previously to turn off necessary exercises were actually antithetical to our position."

- Coronavirus blockade -

North Korea is more isolated than ever after imposing a strict border closure to protect itself from the coronavirus, blockading itself more effectively than any sanctions regime.

The move has hit its already moribund economy and analysts say its authorities are likely to be focused on those domestic issues.

Cheong Seong-chang, director of the Center for North Korean Studies at the Sejong Institute in Seoul, told AFP: "We shouldn't identify every North Korean missile test as a provocation since the South also carries out such tests in regular military exercises."

But he added: "Pyongyang could elevate the intensity of missile tests from short-range to medium-range in the months ahead if it thinks Washington is doubling down on punitive policy against it."