The final NATO summit comes when diplomatic tensions build up over shipments of goods to Kaliningrad.
Lithuania was receiving major threats from Moscow after it had blocked Russia from using the railways to transport coal, metals and other goods sanctioned in military enslavement.
In a direct warning to the Kremlin, Stoltenberg said: “I am sure that Moscow, President Putin, understands our collective security guarantees, understands the consequences of attacking a NATO allied country.
“It will trigger a full Alliance response.”
At the summit, NATO will also drastically change its view of Russia from Moscow’s current description as a strategic partner.
Russia would be designated as the “most direct and immediate threat to our security,” Stoltenberg said of the language to be adopted as part of the “Strategic Concept,” NATO’s plan for the next decade.
The Secretary-General poured cold water on hopes that Sweden and Finland would be admitted to the alliance at the summit.
He said he would host talks between Turkey and the Nordic nations in Madrid, but warned against an immediate breakthrough in Ankara’s opposition to its incorporation.
“I will not make any promises or speculate on any specific deadline. The summit has never been a deadline,” Stoltenberg said.
To further strengthen European security, the Western military alliance will announce plans to conduct training missions to bring the Ukrainian armed forces up to NATO standards.
British and American officials have expressed concern that while they are vital, arms shipments will not be enough to ensure Kyiv’s security in the future.