The Kremlin has tried to calm tensions in a feud between Trump and Medvedev that spiraled into nuclear threats.

Russian former President Dmitry Medvedev blamed NATO countries on Monday for the abandonment of a moratorium on short- and medium-range nuclear missiles and said Moscow would take further steps in response.

So far Trump's promises, threats and cajoling have failed to shift the Kremlin's position, and the stubborn diplomatic stalemate remains in place. Meanwhile, Ukraine is losing more territory on the front line, although there is no sign of a looming collapse of its defenses.

President Trump spoke on Tuesday with Ukrainian President Volodymyr Zelensky and discussed the ceasefire ultimatum Trump set for Russian President Vladimir Putin, according to Ukrainian officials. Why it matters: Trump's deadline to Putin will expire on Friday.