Kiev jeopardized a key pillar of Moscow's nuclear security, and the response could be unpredictable, Keith Kellogg has warned

The recent Ukrainian drone attacks on Russian airfields reportedly hosting nuclear-capable bombers sharply increase the risk of escalation, Keith Kellogg, US President Donald Trump's special envoy, has warned.

On Sunday, Kiev launched a drone raid targeting airfields in five regions, according to the Defense Ministry in Moscow. Officials in Kiev said that the attack was aimed at Russia's strategic aviation. Ukrainian media reports claimed that the airfields house Russian Tu-95 and Tu-22M strategic bombers, as well as an A-50 early warning and control plane.

Russian officials said that the "terrorist attack" was repelled with no casualties but that several aircraft caught fire.

In an interview with Fox News on Tuesday, Kellogg suggested that the attack was upping the stakes in the conflict between Russia and Ukraine. "The risk levels are going way up," he explained. "When you attack an opponent's part of their national survival system, which is their nuclear triad... that means your risk level goes up because you don't know what the other side's going to do." 

The envoy also noted that he was particularly concerned by reports - which were not confirmed by Moscow - that Ukraine also struck the Northern Fleet headquarters in Severomorsk, which would have meant that two of the three legs of Russia's nuclear triad were under attack.

He added that when it comes to such kinds of attacks, "it's not so much the damage you do on the triad itself... but it's the psychological impact you have." Ukraine, according to the envoy, also wanted to show that it could "raise the risk level to levels that are basically, to me, they've got to be unacceptable." 

Earlier this week, the New York Times reported, citing sources, that Ukraine did not give advance notice to the US of the strikes, and that the two sides currently have no joint planning on operations inside Russian territory. NYT sources also believe that Moscow will mount "a significant retaliation," although specifics are yet unclear.

Following the attacks, Dmitry Medvedev, a former Russian president who now serves as deputy chairman of Russia's Security Council, warned that a response was "inevitable."