He said that he sees North Korea as his top foreign policy issue and said his administration is consulting with allies and partners about next steps.
Biden also said he is open to diplomacy with North Korea if the end result is North Korea's denuclearization.
"Let me say that, number one, U.N. Resolution 1718 was violated by those particular missiles that were tested -- number one," Biden said at his first official White House press conference. "We're consulting with our allies and partners and there will be responses if they choose to escalate. We will respond accordingly."
"I'm also prepared for some form of diplomacy, but it has to be conditioned upon the end result of denuclearization. So, that's what we're doing right now, consulting with our allies," he added.
When asked if he agreed with former President Barack Obama's assessment to his successor, former President Donald Trump, that North Korea was his top foreign policy concern, Biden simply replied "yes."
A United States government official confirmed to ABC News that North Korea had fired two ballistic missiles into the Sea of Japan Wednesday night and South Korea's joint chiefs of staff confirmed that they were short-range missiles that traveled an estimated 260 miles at an altitude of 37 miles.
"North Korea this morning fired two unidentified projectiles into the East Sea from South Hamkyung Province," the South Korea government said in a statement. "South Korea and US intelligence are analyzing for any additional information."
"While our military has strengthened awareness and monitoring, ROK-US (officials) are closely working together and maintaining readiness," it added.
It took both governments some time after the launch to determine what types of missiles North Korea had launched. At one point a U.S. official told ABC News it may have been a new variant of a medium-range ballistic missile, but it is now believed that they were short-range missiles.
Prior to Biden's comments on Thursday the only official U.S. government response had come from U.S. Indo-Pacific Command.
"We are aware of North Korean missile launches this morning into the East Sea," Capt. Mike Kafka, the spokesperson for INDOPACOM, said in a statement. "We will continue to monitor the situation and are consulting closely with our allies and partners. This activity highlights the threat that North Korea's illicit weapons program poses to its neighbors and the international community. The U.S. commitment to the defense of the Republic of Korea and Japan remains ironclad."
The ballistic missile launches by North Korea were the first in more than a year and the second this week involving some type of North Korean missiles.
This past weekend North Korea fired two short-range cruise missiles sometime, though the launches were not reported by the U.S. until Tuesday.
Biden administration officials downplayed the missile launches from over the weekend.
"We see this action in the category of normal activity," a senior administration official told reporters.
The launches over the weekend were the first since Biden moved into the White House. Defense Secretary Lloyd Austin visited South Korea last week to discuss the situation on the Korean Peninsula.
The previous administration had a fraught relationship with North Korea. Former President Donald Trump held multiple meetings with dictator Kim Jong Un during his time in office, the first president to do so.
Kim has not carried out any long-range missile tests since Trump met with him in 2018, though it did restart smaller missile tests under the Trump administration.
National security adviser Jake Sullivan is scheduled to hold talks in Washington with his counterparts from Japan and South Korea next week on the next steps to take related to North Korea.
ABC News Chief Global Affairs Correspondent Martha Raddatz contributed to this report.