President Joe Biden warned Thursday that Russia could still invade Ukraine within days and Russia expelled the No. 2 diplomat at the U.S. Embassy in Moscow, as tensions flared anew in the worst East-West standoff in decades.

NATO allies accused Russia of misleading the world by saying it was returning some troops to their bases but instead moved in thousands of new ones. The pullout pledge was among Russian gestures this week that briefly cooled temperatures. Russia is believed to have some 150,000 military forces around Ukraine’s borders, raising fears of a new war in Europe.

Tensions also spiked Thursday along the line that separates Ukrainian forces from Russia-backed separatists in the country’s east, with both sides accusing each other of intensive shelling in a long-simmering conflict that has killed 14,000 people.

U.S. Diplomat Expelled from Moscow

In a surprise blow to diplomacy, Russia ordered the deputy chief of mission at the U.S. Embassy in Moscow, Bart Gorman, to leave the country, the State Department said. It called the move “unprovoked” and “an escalatory step.” Russia did not say why he was expelled.

Doubts escalated in the West over what exactly Russia is doing with its troops around Ukraine — including an estimated 60% of the overall Russian ground forces — and about President Vladimir Putin’s overall intentions.

U.S. Secretary of State Antony Blinken went before the U.N. Security Council and described in detail the range of false-flag attacks that Washington believes Moscow might stage to justify invasion. He described any invasion unfolding with barrages of missiles and bombs, cyberattacks, followed by Russian troops advancing on “key targets that have already been identified and mapped out,” although he did not elaborate on evidence of that.

Russia’s intended targets included Kyiv, with its nearly 3 million people, Blinken said.

“Specific groups of people” were also planned targets of any Russian invasion, he said. “We are laying it out in great detail with the hope that by sharing what we know with the world, we can influence Russia to advance the path of war, and choose a different (path) while there’s still time.”

Stark Comments from Biden

Biden’s comments on the Russian threat were some of his starkest to date, suggesting the administration’s perilous assessment of the situation.

Speaking at the White House, he said Washington saw no signs of a Russian withdrawal, and said the threat of invasion remains “very high” because Russia has moved more troops toward the border with Ukraine instead of pulling them out.

“Every indication we have is they’re prepared to go into Ukraine, attack Ukraine,” he told reporters. He said the U.S. has “reason to believe” that Russia is “engaged in a false flag operation to have an excuse to go in,” but did not provide details.

Biden also said he had “no plans” to speak soon with Putin.

Russia held out an offer of diplomacy, handing the U.S. a response Thursday to offers to engage in talks on limiting missile deployments in Europe, restrictions on military drills and other confidence-building measures.

The response, released by the Foreign Ministry, deplored the West’s refusal to meet the main Russian security and demands and reaffirmed that Moscow could take unspecified “military-technical measures” if the U.S. and its allies continue to stonewall its concerns.

At the same time, it said Russia was ready to discuss limits on missile deployments, restrictions on patrol flights by strategic bombers and other confidence-building steps.

Western Powers Scrambling to Prepare

Russia denies it is plotting an invasion but says it’s free to deploy troops wherever necessary to counter NATO threats. It wants the West to keep Ukraine and other former Soviet nations out of NATO, halt weapons deployments near Russian borders and roll back forces from Eastern Europe — demands the allies have flatly rejected.

Meanwhile Western powers scrambled to avert, or prepare for, eventual invasion.

NATO’s defense ministers in Brussels discussed ways to bolster defenses in Eastern Europe, while EU leaders huddled over how to punish Russia if it invades. The U.N. Security Council met over Ukraine, ahead of the Munich Security Conference in Germany where Ukraine is high on the agenda.

“We cannot afford to fail,” U.N. Undersecretary-General Rosemary DiCarlo said. “The current situation is extremely dangerous.”

China, a key Russian geopolitical ally, accused Washington of “playing up and sensationalizing the crisis and escalating tensions.” Foreign Ministry spokesman Wang Wenbin said the U.S. should “take seriously and address Russia’s legitimate and reasonable concerns on security assurance.”

At NATO headquarters in Brussels, U.S. Defense Secretary Lloyd Austin questioned the Russian troop promises.

“We’ve seen some of those troops inch closer to that border. We see them fly in more combat and support aircraft,” he said. “We see them sharpen their readiness in the Black Sea. We even see them stocking up their blood supplies. You don’t do these sort of things for no reason, and you certainly don’t do them if you’re getting ready to pack up and go home.”

British Defense Secretary Ben Wallace said the West has seen “an increase of troops over the last 48 hours, up to 7,000.” That squared with what a U.S. administration official said a day earlier. The top EU official said similar.

Russian Buildup Continues Near Ukraine

Maxar Technologies, a commercial satellite imagery company that has been monitoring the Russian buildup, reported continued heightened military activity near Ukraine. It noted a new pontoon bridge and a new field hospital in Belarus.

British Armed Forces Minister James Heappey called Russia’s claim to be withdrawing troops “disinformation.” Russia leveled that charge against the West.

Noting Russian video of troop movements, NATO Secretary-General Jens Stoltenberg said: “The fact that you’re putting a battle tank on a train and moving it in some direction doesn’t prove a withdrawal of troops.”

Russian Defense Ministry spokesman Maj.-Gen. Igor Konashenkov offered a bit more detail Thursday, saying that Russian tank and infantry units that engaged in drills in the Kursk and Bryansk regions neighboring Ukraine were returning to their permanent bases in the Nizhny Novgorod region. He said that some already were at their bases after a 700-kilometer journey.

Troops deployed for exercises in Crimea, which Russia annexed from Ukraine in 2014, have moved back to Chechnya and Dagestan in Russia’s North Caucasus, he said. He added that Russian troops involved in drills in Belarus also will move back to their garrisons after war games there wrap up Sunday. Konashenkov didn’t mention how many troops were deployed and didn’t say how many returned.

NATO, meanwhile, has moved troops and military equipment into Eastern Europe in a display of resolve of meant to deter any Russian aggression and underline its intent to defend NATO’s eastern members, in the unlikely event that they too become a target.

U.S. Deploys Troops to Poland

The U.S. has started deploying 5,000 troops to Poland and Romania. Another 8,500 are on standby, and some U.S. troops are expected to move toward Bulgaria. Britain is sending hundreds of soldiers to Poland, offering more warships and planes, and doubling its personnel in Estonia. Germany, the Netherlands and Norway are sending additional troops to Lithuania. Denmark and Spain are providing jets for air policing in the Baltic Sea region, and Spain deployed to Bulgaria.

Even if an attack doesn’t materialize, the sustained Russian pressure on Ukraine has further hobbled its shaky economy and left an entire nation under constant strain.

Eastern Ukraine already has been the site of fighting since 2014, and tensions soared again Thursday.

Separatist authorities in the Luhansk region reported an increase in Ukrainian shelling along the tense line of contact. Separatist official Rodion Miroshnik said rebel forces returned fire.

Ukraine disputed the claim, saying separatists had shelled its forces, but they didn’t fire back. The Ukrainian military command charged that shells hit a kindergarten in Stanytsia Luhanska, wounding two teachers, and cut power supply to half of the town.

An observer mission of the Organization for Security and Cooperation in Europe is expected to offer its assessment of the situation later Thursday.

Ukrainain President Volodymyr Zelenskyy tweeted that the kindergarten shelling “by pro-Russian forces is a big provocation,” adding that the OSCE monitoring activities are “an additional deterrent.”

Asked about the flare-up, Stoltenberg said NATO was concerned “that Russia is trying to stage a pretext for an armed attack against Ukraine.”

Russia, in turn, aired worries that hawkish forces in Ukraine, encouraged by the West, could launch an attack to reclaim control of the rebel areas — plans Kyiv denies.

A 2015 deal brokered by France and Germany helped end the worst of the fighting in eastern Ukraine, but regular skirmishes have continued and a political settlement has stalled.

Blinken and U.S. Vice President Kamala Harris were among political, military and diplomatic leaders heading to the annual security conference in Munich that will see urgent consultations on the crisis.