KYIV, Ukraine (AP) — Ukrainian forces claimed Thursday to have shot down a Russian attack helicopter in eastern Ukraine near the eastern Ukraine city of Avdiivka, where soldiers are fighting from street to street as Russia's army steps up its four-month campaign to surround Kyiv’s defending troops. Ukrainian soldiers used a portable anti-aircraft missile to take down the Ka-52 Alligator attack helicopter, one of the Russian air force’s deadliest weapons, according to Oleksandr Tarnavskyi, the commander of Ukrainian units fighting on the southeastern front line. The roughly 1,500-kilometer (930-mile) line of contact has shifted little during recent months of wintry weather.