Previous Trump promises, threats and cajoling have failed to yield results., and the stubborn diplomatic stalemate will be hard to clear away. Meanwhile, Ukraine is losing more territory on the front line, although there is no sign of a looming collapse of its defenses.

The Kremlin said on Tuesday that it had "taken note" of a statement by U.S. President Donald Trump that he was shortening his deadline for Moscow to sign up to a ceasefire in Ukraine or face sanctions.