KHARKIV, Ukraine (Reuters) – Thousands took to the streets of Ukraine’s second-largest city on Saturday carrying banners saying “Kharkiv is Ukraine” and “stop Russian aggression”, as the country braced for a possible military offensive from Russia. Weeks of diplomacy between the West and Moscow have produced no breakthrough after Russia massed tens of thousands of troops near Ukraine’s borders. Moscow denies it plans to attack Ukraine but has demanded security guarantees, including a block on Ukraine joining the NATO alliance. Kharkiv, an eastern industrial city that lies 42 km (26 miles) from…