The United States said on Monday it was Russia that is escalating the conflict in Ukraine by deploying North Korean troops, after the Kremlin warned that Washington would deepen its involvement in the war by allowing Kyiv's forces to strike far into Russia with U.

Russia is paying $2,000 a month for each North Korean soldier, per reports. But the soldiers, who could number 100,000, probably won't see any of it.

North Korea ratified a major defence pact with Russia on Tuesday, outlining mutual military aid and requiring both countries to provide each other with immediate military assistance if attacked. Russia had already completed its side of the ratification last week after the pact was signed by Russian President Vladimir Putin and North Korean leader Kim Jong Un.