Moscow (AFP) – The United States stepped up warnings of an imminent Russian invasion of Ukraine on Thursday, despite Moscow’s continued denials and announcements of troop withdrawals from near the border. Adding to the already fierce tensions, Ukraine and Moscow-backed separatists traded accusations of intensifying shell fire across their frontline, with Western officials saying Moscow was looking to create a pretext for an invasion. The threat of an invasion is “very high, because they have not moved any of their troops out. They’ve moved more troops in,” US President Joe Biden told reporters…