President Trump has given an ultimatum to President Vladimir V. Putin of Russia to end the war in Ukraine or face U.S. sanctions.

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 Russian president says Moscow's initial tough demands must be met, despite a looming US sanctions deadline.