Russia's growing economic and military cooperation with China, North Korea and Iran is threatening Europe, the Indo-Pacific and North America, NATO Secretary General Mark Rutte said on Tuesday.

"The deepening military cooperation between Russia and North Korea is a threat to both the Indo-Pacific and Euro-Atlantic security," NATO Secretary-General says.

"Today I can confirm that over 10,000 (North Korean) soldiers have been sent to eastern Russia, and most of them have moved to the far western Kursk Oblast, where they have begun engaging in combat operations with Russian forces,

The United States opened a new air defence base in northern Poland on Wednesday, an event the European nation's president said showed the country was secure as a member of NATO even as Russia wages war in neighbouring Ukraine.

"The Polish-American alliance is strong, regardless of who governs in Warsaw and Washington," Polish Foreign Minister Radoslaw Sikorski said.

A long-planned US missile defence base was officially opened in northern Poland on Wednesday. The military base in Redzikowo is located about a hundred kilometres west of Gdansk and is part of NATO's missile defence system on the continent.