US President Joe Biden said on Thursday that the United States will respond appropriately should North Korea continue to escalate tension, but that it is also prepared for diplomacy with the recalcitrant regime.

Biden noted the launch of the missiles on Thursday (Seoul time) was in violation of UN Security Council resolutions.

"Let me say that, number one, UN resolution 1718 was violated by those particular missiles that were tested," Biden said in his first formal press conference since taking office on Jan. 20. "We are consulting with our allies and partners, and there will be responses if they choose to escalate. We will respond accordingly," he added.

North Korea launched what appeared to be short-range ballistic missiles into the sea between the Korean Peninsula and Japan, US and South Korean military officials said earlier.

Pyongyang is prohibited from testing any type of ballistic missiles under the UN Security Council resolution.

Biden's remarks marked the first official reaction from Washington to the North's latest missile launch.

Pyongyang fired two cruise missiles on Sunday, which Biden had shrugged off as "business as usual."

"We've learned nothing much has changed," Biden said of the cruise missiles, which, according to US officials, are not "covered" or prohibited by UN Security Council resolutions on North Korea.

Biden said diplomacy is still possible, despite the North's launch of ballistic missiles in violation of the UN resolution.

However, diplomacy, he said, "has to be conditioned upon the end result of denuclearization."

Many North Korea observers believe Pyongyang may have precisely timed its first serious provocation in over a year to take place just before Biden's first press conference.

North Korea last launched a ballistic missile in March 2020.

North Korea experts have long warned that Pyongyang may try to force itself onto the agenda of the new Biden administration by staging military provocations such as missile launches.

"In the months ahead, we should expect the North Koreans to test bigger and more advanced missiles," said Harry Kazianis, senior director of Korean Studies at the Center for the National Interest think tank. "We should also expect a fiery response when the Biden North Korea policy is announced, which likely will be a pressure strategy to get the Kim regime to give up its nuclear weapons."

The US is undertaking a comprehensive review of its North Korea policy, and senior administration officials have said the review is now in its final stages.

Next week, National Security Adviser Jake Sullivan will host his South Korean and Japanese counterparts in Washington to discuss the outcome of the North Korea policy review and their next steps, the officials said earlier.

North Korea has maintained a self-imposed moratorium on nuclear and long-range missile tests since November 2017, about two months after it conducted its sixth nuclear test.

However, North Korean leader Kim Jong-un said last year that he no longer felt bound by such restrictions. (Yonhap)