Russian nuclear submarines sailed off for drills in the Barents Sea, and mobile missile launchers roamed snow forests in Siberia on Tuesday, after President Vladimir Putin ordered his country’s nuclear forces to be on high alert due to tensions with the West over Ukraine’s invasion.

The Northern Fleet of Russia said in a statement that several of its nuclear submarines were participating in exercises to “train maneuvering in stormy conditions.” It said several warships tasked with protecting northwest Russia’s Kola Peninsula, which is home to several naval bases, would take part in the exercises.

The Strategic Missile Forces dispersed Yars intercontinental ballistic missile launchers in forests in the Irkutsk region of eastern Siberia to practice secret deployment, according to a statement from the Defense Ministry. The military did not say whether the drills were related to Putin’s Sunday order to place the country’s nuclear forces on high alert in the midst of Russia’s war in Ukraine. It was also unclear whether the exercises marked a shift in the country’s normal nuclear training activities or posture.

Putin’s decree applied to all components of Russia’s nuclear triad, which includes nuclear submarines armed with intercontinental ballistic missiles, nuclear-tipped land-based ICBMs, and nuclear-capable strategic bombers, as in the United States. By far the two largest nuclear arsenals in the world are those of the United States and Russia.

The United States said Putin’s move exacerbated an already dangerous conflict, but it has yet to announce any changes to its nuclear weapons alert level, possibly because it was unclear what the Russian president’s order meant in practice.

The land- and submarine-based segments of Russia’s and the United States’ strategic nuclear forces are always on alert and ready for combat, but nuclear-capable bombers and other aircraft are not. One party increasing bomber nuclear-combat readiness or ordering more ICBM-carrying submarines to sea would raise red flags for another.

In comparison to the United States, Russia places a greater emphasis on nuclear-tipped intercontinental ballistic missiles, which are stored in silos or mounted on mobile launchers. A change in their readiness status could be more difficult to spot and assess.

Putin’s order heightened already heightened tensions, drawing comparisons to the 1962 Cuban Missile Crisis, which saw Moscow and Washington on the verge of nuclear war.

In making his decision, Putin cited “aggressive statements” from NATO allies as well as new, crippling Western sanctions that froze Russia’s hard currency reserves, an unprecedented move that threatened to devastate the country’s economy and finances.

According to the most recent statements from Putin and other Russian officials, the Kremlin regards Western sanctions as a threat on par with military aggression.

Dmitry Medvedev, a deputy head of Russia’s Security Council, responded on Tuesday to French Finance Minister Bruno Le Maire’s remark that the European Union would launch an all-out economic and financial “war” against Russia.

“Today, some French ministers said that they declared an economic war on Russia,” said Medvedev, who served as Russia’s interim president from 2008 to 2012, when Putin was forced to step down as prime minister due to term limits. “Gentlemen, watch your tongue!” And don’t forget that in human history, economic wars have frequently escalated into actual wars.”