By Natalia Zinets and Max Hunder KYIV (Reuters) -The war in Ukraine could last for years, the head of NATO said on Sunday, calling for steadfast support from Ukraine’s allies as Russian forces battle for territory in the country’s east. Secretary-General Jens Stoltenberg said supplying state-of-the-art weaponry to Ukrainian troops would boost the chance of freeing its eastern region of Donbas from Russian control, Germany’s Bild am Sonntag newspaper reported. After failing to take the capital Kyiv early on in the war, Russian forces have focused efforts on trying to take complete control of th…