NEW YORK -- It's still "too soon to know" whether the Russian government was behind Monday's cyberattacks on over a dozen U.S. airports, according to White House National Security Council spokesman John Kirby.
"We just don't really understand fully who's behind this, what the motivation was, certainly at what level -- if any -- Kremlin officials were aware. We just don't know," Kirby told ABC News' George Stephanopoulos in an interview Tuesday on "Good Morning America."
"We're grateful that no airport operations were affected, no safety was put at risk, but we're looking into this," he added. "We're going to investigate this, we're going to try to get to the bottom of it and obviously we take cyber resilience very, very seriously, regardless of what happened at these airports."
Some of the nation's largest airports were targeted for cyberattacks by someone within Russia on Monday, according to a senior U.S. official briefed on the situation. The systems targeted do not handle air traffic control, internal airline communications and coordination or transportation security.
"It's an inconvenience," the source told ABC News, adding that the attacks have resulted in targeted "denial of public access" to public-facing web domains that report airport wait times and congestion.
More than a dozen websites for U.S. airports were impacted by the "denial of service" attacks, which essentially overload sites by jamming them with artificial users, according to John Hultquist, head of intelligence analysis at American cybersecurity firm Mandiant. Hultquist told ABC News that such cyberattacks are highly visible but largely superficial and often temporary.
A pro-Kremlin hacker group called Killnet is believed to be behind Monday's attacks, according to Hultquist. Killnet has been active since Russia invaded neighboring Ukraine on Feb. 24, with the hackers targeting Ukrainian allies and recently claiming credit for taking down U.S. government websites. The groups operates internationally and has been known to carry out cyberattacks across Europe, according to cybersecurity experts.
While similar groups have been found to be fronts for state-backed actors, Hultquist said there is no evidence that the Russian government was involved in directing Monday's attacks.
Both the FBI and the Cybersecurity and Infrastructure Security Agency, which is part of the U.S. Department of Homeland Security, said they were aware of the cyberattacks.
ABC News' Josh Margolin, Quinn Owen and Sam Sweeney contributed to this report.