The United States said Thursday that Russia is on the verge of unleashing a massive military attack against Ukraine, dismissing Moscow's claim to be pulling forces back, as artillery fire hit a Ukrainian kindergarten.
In a dramatic, previously unscheduled speech to the United Nations in New York, US Secretary of State Antony Blinken said intelligence showed Moscow could order an assault on its neighbor in the "coming days."
"Demonstrate it by sending your troops, your tanks, your planes, back to their barracks and hangers," he said.
Russia denies any invasion plans but warned of "military-technical measures" if its far-reaching demands for a US and NATO pullback from eastern Europe aren't satisfied.
The United States said late Thursday that Blinken and his Moscow counterpart Sergei Lavrov had agreed to meet next week -- provided there was no invasion before then.
Keeping up the pressure, President Joe Biden accused Moscow of preparing a "false flag operation" as a pretext for an attack.
"They have not moved any of their troops out. They've moved more troops in," Biden said. "Every indication we have is that they're prepared to go into Ukraine."
Biden will hold a phone meeting Friday with the leaders of Germany, Britain, France, the European Union and NATO to discuss the Ukraine crisis.
- 'Forced to respond' -
Russia has massed enormous air, land and sea forces around Ukraine. President Vladimir Putin and officials say the troops are only conducting practice exercises.
However, Putin has made clear that the price for removing any threat would be Ukraine agreeing never to join NATO and for the Western alliance to pull back from a swath of eastern Europe, effectively splitting the continent into Cold War-style spheres of influence.
The United States said that it had received Putin's response to its offers of a diplomatic solution to the crisis, but did not give any reaction to the contents.
The Russian foreign ministry indicated that there was little to discuss.
"In the absence of will on the American side to negotiate firm and legally binding guarantees on our security from the United States and its allies, Russia will be forced to respond, including with military-technical measures," the foreign ministry said.
"We insist on the withdrawal of all US armed forces in Central Europe, Eastern Europe and the Baltics."
Russia also expelled the number two US diplomat in Moscow, the US State Department said, condemning the "unprovoked" action.
- Artillery fire on kindergarten -
Russia took over Ukraine's Crimea region and began backing heavily armed separatists in the eastern Donetsk and Lugansk regions in 2014, sparking a war that has already cost thousands of lives.
Sporadic fighting remains common in the east, and the Ukrainian army accused the pro-Russian separatists of 34 ceasefire breaches on Thursday, 28 of them using heavy weapons.
The potentially most serious incident -- an example of the kind of spark that many fear could ignite far more intense fighting -- was the shelling of a kindergarten in the village of Stanytsia-Luganska. Children were inside but none were hit.
Ukrainian President Volodymyr Zelensky tweeted that the attack "by pro-Russian forces is a big provocation."
Russian news agencies quoted authorities in the separatist Lugansk region saying they blamed Kyiv after the situation on the frontline "escalated significantly."
Western capitals say they are also concerned by the Russian parliament's request that Putin grant unilateral recognition of independence for the separatists in eastern Ukraine.
"If this request were accepted, it would... demonstrate a Russian decision to choose a path of confrontation over dialogue," British Foreign Secretary Liz Truss said.
Putin earlier this week claimed with no evidence that Ukraine is committing "genocide" in the eastern region.
- Disputed withdrawal -
Moscow has made several announcements of troop withdrawals this week and on Thursday said that tank units had begun returning to their bases from near Ukraine.
The United States, NATO and Ukraine all said they had seen no evidence of a pullback, with Washington saying Russia had in fact moved 7,000 more troops near the border.
According to US officials, there are now about 150,000 Russian troops arrayed in offensive groupings on the southern, eastern and northern borders of Ukraine.