The Kremlin is weighing options for a concession to US President Donald Trump that could include an air truce with Ukraine to try to head off the threat of secondary sanctions, even as Russia remains determined to continue its war.

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.