Washington (AFP) - US Army troops equipped with tanks will head to Eastern Europe soon to reassure NATO allies anxious over Russia's intervention in Ukraine, Pentagon officials said Thursday.

About 600 troops from the 1st Brigade, 1st Cavalry Division are due to deploy in October to Poland and the Baltic states for training exercises with alliance members, replacing paratroopers from the 173rd Airborne Brigade, said spokeswoman Lieutenant Colonel Vanessa Hillman.

"It's a three month rotation," Hillman said. The drills are "focused on small unit and leader training."

Unlike the outgoing unit, the troops from the "Iron Horse brigade," based in Fort Hood, Texas, will deploy with M-1 Abrams tanks and infantry fighting vehicles, she said.

US commanders have organized an array of exercises and training efforts on NATO's eastern border to reassure allies dismayed over Russia's support of separatists in Ukraine. Washington also has sent F-16 fighter jets to Poland and joined air policing missions over the Baltic states.

Kiev and Western countries on Thursday accused Russia of directly entering the fighting in eastern Ukraine, saying Moscow had sent combat units into the former Soviet state.

As the UN Security Council prepared to hold an emergency meeting on the crisis, NATO said at least 1,000 Russian troops were on the ground backing pro-Moscow separatists who are fighting Kiev government forces.

NATO leaders have said the alliance must reevaluate its strategy and its troop deployments in light of the conflict in Ukraine.