Ukraine’s military and the Russian-backed separatists it has battled for eight years in the country’s eastern Donbas region both accused the other side of opening fire on Thursday in violation of ceasefire agreements that have been shaky, at best, since they were signed seven years ago. As the reported shelling raised tensions — and despite Russia’s claims to be pulling forces back from Ukraine’s borders — the Biden administration said “evidence on the ground” showed Russia was “moving toward an imminent invasion” of its neighbor.

The United States and its NATO partners have dismissed Moscow’s assertions of an initial force drawdown along Ukraine’s northern, eastern and southern borders, saying that President Vladimir Putin’s military appears, in reality, to be bolstering troop numbers, not reducing them.

America and its allies have also warned for weeks that Russia could try to stage a “false-flag” incident — including a faked attack by Ukrainian forces on the rebels in Donbas — to use as a pretext to invade Ukraine. On Thursday, amid the claims of shelling from both sides, NATO Secretary Jens Stoltenberg said the alliance was “concerned” that Russia was trying to do just that.