NATO’s top military commander said the alliance is “ready to fight tonight” if it is attacked, while European officials warn that Russia could test NATO’s defenses through increased covert attacks or a limited military incursion.

In recent months, European nations have faced a rise in covert Russian activity, including an arson attack on an Estonian defense company and a failed attempt to attack a Ukrainian aircraft at a German airport.

If Russia decides to attack NATO, the alliance will respond by using sensors, autonomous systems and military force to stop any assault, NATO’s Supreme Allied Commander U.S. General Alexus Grynkewich said in Warsaw Monday.

Addressing the Warsaw Security Forum, Grynkewich laid out what he termed NATO’s “Theory of Victory.”

The NATO commander stated that he does not regard a conflict as either imminent or inevitable, and that the most effective means of preserving peace is to prepare for war while sustaining open channels of communication in order to “resolve misunderstandings.”

Grynkewich gave no specific details about what kind of attack NATO is preparing for, nor where, nor with what kind of forces.

But outlining what a response to a Russian attack could look like, Grynkewich said NATO's combined land, sea and air forces will move to stop Moscow seizing territory and deny Russia the ability to hold ground.

"My theory of victory is simple," he declared to the Warsaw conference.

We will block the initial attack.

If the attack continues, we will blunt it and stop any enemy advance.

And if needed, we will break the enemy's forces and the operational war-fighting system arrayed against us.

That encompasses not merely the attacking force but every element that supports, sustains and controls it, he said.

In recent weeks, senior European officials and intelligence services have warned that Russia may be planning to test the NATO alliance through increased covert attacks or even an incursion, following a spate of sabotage incidents across the continent.

Denmark’s defense intelligence service specifically warned that Russia could use such tactics to split the NATO alliance.

But at the same time, President Donald Trump has also sent shock waves through Europe by agreeing to a deal to buy diesel from Russia in an attempt to lower prices in the U.S. ahead of the midterm elections.

Earlier this year, the U.S. president said he was pulling American troops out of Europe, and his war with Iran has caused critical shortages of advanced air defense missiles in Europe.

“Ultimately it’s a political decision,” as to where troops are deployed, but “no one should question the U.S. commitment to the alliance,” Grynkewich said.

Grynkewich stressed that it was important for alliance members to coordinate a “coherent” response to Russian activity, so as to make clear to Moscow “where our red lines are.”

The response to increased Russian malign activity and sabotage, he said, should be to redouble support for Ukraine.

While Polish Prime Minister Donald Tusk warned that Russia is planning to escalate with drone or rocket strikes on European allies supporting Ukraine, other countries have called for calm.

Denmark’s Defense Intelligence Agency said there is a “low but growing risk” that Russia will launch a limited military attack against one or several NATO countries bordering Russia.

NATO does not seek war with anyone, yet it will detect an impending military attack and “is unlikely to be caught by surprise,” Grynkewich said.

Although Grynkewich said NATO would defend against any attack by Russia using a network of sensors and autonomous systems, some NATO nations have previously struggled to perform in exercises simulating drone warfare.

They have also faced challenges detecting and responding to incursions of drones which have entered their airspace.

Multiple attack drones have crashed across NATO member states bordering Russia, Ukraine and Belarus.

Moreover, in May, residents of the Lithuanian capital, Vilnius, were instructed to seek shelter after a drone strayed into Lithuanian airspace.

When asked whether NATO could deter Russia in the way Grynkewich described, his spokesperson, Col. Martin O’Donnell, said NATO nations are increasingly deploying ground sensors and other technology to detect and counter drones.

The network that connects systems to shoot down drones and sensors is in the process of being established, although they have not yet taken down any drones, he said.

In September, Germany accused Russia of orchestrating a plot at Leipzig airport to deploy a drone laden with explosives against a Ukrainian aircraft.

British officials likewise asserted that they had foiled a Russian plot targeting a drone facility outside London, while Estonian officials attributed a fire at a defense company to Russia.

The incidents are among at least 211 that Western officials have blamed on Russia since Moscow's invasion of Ukraine and that Reporters has tracked.

In its assessment released earlier in September, Denmark’s defense intelligence service suggested that Russia might try to obtain Ukrainian drones and use them to attack Europe, so as to hide any Russian involvement.

Tusk suggested that Russia would likely present any attacks as “accidental” in order to “paralyze or at least weaken the motivation of NATO countries” to rush to the defense of a member state coming under attack.

The Danish service said the aim of any such attack would be to divert European resources away from supporting Ukraine and sow division in NATO.

But both the Danish service and O’Donnell said while Russia is fighting in Ukraine, it would be difficult to launch an outright attack on NATO.