By Alexander Marrow and Aleksandar Vasovic MOSCOW/KYIV (Reuters) -The United States and NATO said Russia was still building up troops around Ukraine on Wednesday despite Moscow’s insistence it was pulling back, questioning President Vladimir Putin’s stated desire to negotiate a solution to the crisis. In Ukraine, where people raised flags and played the national anthem to show unity against fears of an invasion, the government said a cyberattack that hit the defence ministry was the worst of its kind the country had seen. It pointed a finger at Russia, which denied involvement. White House pre…