NATO allies are alarmed and will respond to a rising campaign of hybrid attacks against them by Russia, US Secretary of State Antony Blinken said Friday.

Speaking after two days of talks in Prague among NATO foreign ministers, Blinken said: "Virtually every ally was seized with this intensification of Russia's hybrid attacks.

"We know what they're up to, and we will respond both individually and collectively as necessary," Blinken told reporters.

Blinken pointed to a series of incidents short of military strikes against the 32-member transatlantic alliance, which considers an attack on one an attack on all.

Russia last week removed buoys demarcating the border with Estonia in the River Narva.

Blinken also pointed to incidents inside NATO of "setting fire and sabotaging supply warehouses" as well as growing cyber attacks and disinformation campaigns attributed to Russia.

Estonian Foreign Minister Margus Tsahkna this week told AFP that Russia was "pushing the limits and also playing with our fears".

NATO earlier this month condemned Russian "malign activities" on its territory, saying actions like disinformation, sabotage, violence and cyberinterference threatened the alliance's security.

Authorities in the Czech Republic, Estonia, Germany, Latvia, Lithuania, Poland and Britain have recently investigated and charged people in connection with "hostile state activity".

The incidents come as Russia mounts an offensive in northeastern Ukraine, scoring battlefield victories more than two years into its invasion.

Blinken confirmed that President Joe Biden has approved Ukrainian requests to use US weapons to strike Russian forces involved in the offensive even if they are immediately across the border.

The top US diplomat repeated his warning that a victory by Russia would embolden not only Moscow but other "would-be aggressors".

"We know that if Russia's aggression is allowed to proceed in Ukraine with impunity, it will not stop with Ukraine," Blinken said.