Shelling, evacuations fuel tensions on Russian-Ukrainian border

Ukrainian soldiers are wary of being drawn into a clash with Moscow-backed separatists that could serve as a pretext for Russian invasion

Artillery shelling in the east of Ukraine and orders from Russian-backed separatists for civilians to evacuate the region ratcheted up already crackling tensions over the massing of Russian troops Friday ahead of what the United States says is a likely invasion.

However, the United States says that with an estimated 149,000 Russian troops on Ukraine's borders -- as many as 190,000, when including the Russian-backed separatist forces -- it's likely not a matter of if there'll be a large-scale attack, but when.