European countries have sounded the alarm over what they see as rising Russian malign activity, including sabotage of railway lines in Poland, arson and cyber attacks.

The growing concern has led to calls from some hawkish NATO members for the alliance to take a more aggressive approach to Moscow's meddling.

"This doesn't represent an existential threat to anything that the alliance is doing. It's not undermining our unity. We're able to respond and manage this," US General Alexus Grynkewich, NATO's supreme allied commander in Europe, told journalists.

But he said that "we also do think about being proactive".

"If Russia is attempting to provide dilemmas to us, then maybe there are ways that we could provide dilemmas to them. And I'll just leave it at that because I don't want to get into the specifics," he said.

The US commander, appointed to the post this year by President Donald Trump, stressed however that NATO remained a "defensive alliance".

"There's nothing offensive about this," he said.

Western officials have accused Russia of waging a campaign of "hybrid warfare" on NATO territory to destabilise their countries as the war in Ukraine drags on.

"Those hybrid threats are a real issue, and I do think that we can anticipate more of that happening," Grynkewich said.

He described the string of incidents as part of a "hybrid network" and argued that NATO had to respond to them regardless of whether they were "reckless" or intentional.

"First off, I think it's important that we attribute it and that we say that we know that Russia is behind some of this, maybe not all of it, but certainly some of it. And our public should know that," he said.