Poland scrambled fighter jets and an early warning aircraft, and put its ground air defenses and radar systems on "the highest state" of alert.

The strikes, which were the latest in Russia’s almost daily attacks on the Ukrainian power grid as bitter winter temperatures approach, killed at least six people, including a 7-year-old girl, according to authorities. Children between 2 and 16 years of age were among the 18 injured.

The United States has informed NATO allies that it will reduce its troop presence along Europe’s eastern border with Ukraine