"These actions threaten regional and international security," UN spokesman Stephane Dujarric said.
State-run Korean Central News Agency said the North's leader Kim Jong-Un oversaw yesterday's missile test, which has sparked a fresh chorus of international condemnation and threats of tougher UN sanctions.
Researchers have said that some of the code used in Friday's ransomware, known as WannaCry software, was nearly identical to the code used by the Lazarus Group, a group of North Korean hackers who used a similar version for the devastating hack of Sony Pictures Entertainment in 2014 and the last year's hack of Bangladesh Central Bank.
"This action is in violation of Security Council resolutions and a threat to peace and security in the region," Guterres said in a statement issued by his spokesman.
In a statement, the powerful ministry of state security said it had foiled a "vicious plot" by a "hideous terrorists' group" to attack the North's "supreme leadership".
During their conversation, the two leaders also discussed at length working together to eradicate terrorism throughout the Middle East and spoke about how best to resolve the "very dangerous" situation in North Korea, the White House said yesterday.
"There's a lot of things that go along with that, and that's the key thing. "Under the right circumstances" was, I believe, the phrase he used. I think that is something in keeping with our consistent with the policy expressed by Secretary of State Rex Tillerson as well," White House Press Secretary Sean Spicer told reporters at his daily news conference yesterday.
Japanese Prime Minister Shinzo Abe today called North Korea's test-fire of a ballistic missile "absolutely unacceptable" and a "grave threat to our country".
"The US Pacific Command detected what we assess was a North Korean missile launch at 10:33 AM Hawaii time, April 28. The ballistic missile launch occurred near the Pukchang airfield," Dave Benham, United States Pacific Command spokesman, said in a statement.
The United States is not ruling out direct dialogue with North Korea on its nuclear programme, Secretary of State Rex Tillerson said in an interview with National Public Radio.
"There is a chance that we could end up having a major, major conflict with North Korea," Trump said in an interview at the Oval Office.
"The leaders discussed the conflicts in Syria and Yemen and the urgent security challenge posed by North Korea," the White House said in a readout of the phone call.
"(China) hopes that the relevant parties can maintain restraint and avoid actions that would increase tensions in the Korean Peninsula," Xi said, according to state broadcaster CCTV.
US President Donald Trump ordered the USS Carl Vinson carrier strike group to sail to waters off the Korean peninsula in response to rising tension over the North's nuclear and missile tests, and its threats to attack the United States and its Asian allies.
Secretary-General Antonio Guterres told reporters the United Nations fully backs efforts of all states trying to ensure "that North Korea doesn't acquire the capacities that would become a threat, not only for the region but in a wider area of the world."
Spot gold was up 0.5 percent at USD 1,291 per ounce as of 0239 GMT, after hitting its highest since early November at USD 1,295.42.
Benchmark Brent crude futures were down 49 cents at USD 55.40 at 0310 GMT. On Thursday, before the break closed most major markets, they settled up 3 cents at USD 55.89 a barrel.
It has placed China, Germany, Japan, Korea, Switzerland and Taiwan in the monitoring list in its six-monthly report to the Congress.
"We're prepared to respond to an all-out war with an all-out war and we are ready to hit back with nuclear attacks of our own style against any nuclear attacks," Choe Ryong-Hae said.
North Korean state media on Tuesday warned of a nuclear attack on the United States at any sign of a US pre-emptive strike as a US Navy strike group led by a nuclear-powered aircraft steamed towards the western Pacific.
The Carl Vinson strike group cancelled a planned trip to Australia this weekend to head to the region, in a show of force as Washington signalled it may act to shut down Pyongyang's nuclear capabilities.
Top aides to U.S. President Donald Trump differed on Sunday on where U.S. policy on Syria was headed after last week's attack on a Syrian air base, while U.S. Secretary of State Rex Tillerson warned the strikes were a warning to other nations, including North Korea.
The Kospi was down by 0.52 percent, with China-exposed stocks pressured following heightened tensions in the Korean peninsula. Shares for Lotte Shopping, the retail arm of conglomerate Lotte, fell by 1.59 percent, while shares of LG Electronics plunged 1.97 percent.
Xi and Trump are scheduled to have a series of meetings later in the day at the US President's Mar-a-Lago residence in Florida, which is now being called the Southern White House.