Thousands of Russian troops on Thursday began 10 days of exercises in Belarus, and Ukraine warned of upcoming Russian naval drills so extensive they would block shipping lanes, as the Kremlin continued to tighten its military vise on Ukraine.

In Moscow, Russia’s top diplomat, Foreign Minister Sergey Lavrov, gave a bleak assessment of the diplomatic efforts aimed at deterring a full-scale invasion. He dismissed his talks with his British counterpart as a conversation of a “mute person with a deaf person,” asserting again that the West was not seriously addressing Russia’s most pressing concerns.

President Vladimir Putin of Russia was slightly more conciliatory, telling reporters on Thursday that negotiations with the West were continuing over Russia’s demands to reshape the security architecture of Eastern Europe. He said Russia was preparing written responses in its back-and-forth with the United States and NATO, and added that he planned to speak by phone in the coming days with President Emmanuel Macron of France.

But the intensifying Russian military activity north, east and south of Ukraine gave an ominous undertone to the diplomatic scramble. Satellite images collected Wednesday and Thursday revealed new deployments of Russian military equipment and troops in Crimea, western Russia and Belarus.

President Joe Biden, warning Americans in Ukraine to leave, told NBC News in an interview Thursday that he would not send troops to rescue remaining US citizens in the event of an invasion, and risk direct conflict with Russian forces. “That’s a world war when Americans and Russia start shooting at one another,” he said.

In Belarus, Ukraine’s northern neighbour and Russia’s closest international ally, Russian fighter jets launched air patrols, and Russia’s potent S-400 air defence systems were deployed near the Ukrainian border. Russian marines normally based in eastern Siberia — more than 2,500 miles away — practiced urban warfare during the drills, the Russian Defence Ministry said.

And off Ukraine’s southeastern coast, in the Black Sea and the Sea of Azov, Russia was preparing to hold large-scale naval exercises — prompting a protest from Ukraine that they would block vital trading routes. Ukraine said the planned drills were “an abuse of international law” by Russia “in order to achieve its own geopolitical goals,’’ and it called on other countries to respond by barring Russian ships from their ports.

Ukraine’s seaports of Odessa, Mykolaiv, Kherson, Mariupol and Berdyansk, which could be disrupted by the Russian military exercises, are gateways for the vast grain exports from Ukraine’s black earth farming zone, along with coal, steel and other commodities important for the country’s economy.

Moscow described all the drills as legal under international law and promised that Russian troops would leave Belarus after the exercises there conclude Feb 20. But Western officials worry that the exercises are a cover to position more Russian forces around Ukraine, giving Putin the ability to launch an invasion on short notice.

Western officials have said they do not believe Putin has made a decision to invade. But combined with Russia’s recent buildup on Ukraine’s eastern border and in Crimea, the troops in Belarus and the amphibious landing ships and other warships gathering off Ukraine’s coast created the sense of a noose tightening around Ukraine.

“This is a dangerous moment for European security,” NATO Secretary-General Jens Stoltenberg said, describing Russia’s military deployment to Belarus as its biggest since the end of the Cold War. “The warning time for a possible attack is going down.”

The joint news conference in Moscow by the top British and Russian diplomats offered a stark display of the clashing worldviews that have made the crisis over Ukraine appear nearly impossible to resolve.

Foreign Secretary Liz Truss of Britain, making a hastily scheduled visit, reiterated Western warnings that an invasion of Ukraine would result in “a prolonged and drawn-out conflict” and that Russia needed to pull back the 130,000 troops that US and Ukrainian officials estimate it had massed near Ukraine’s borders.

Lavrov countered by repeating the Russian government’s contention that it was not threatening anyone, and therefore had no reason to de-escalate.

“You first have to prove to me that we are the ones who created this tense situation,” Lavrov said, rejecting the idea of a Russian invasion as bordering on farce. The West “is trying to make a tragedy out of this, while, increasingly, it’s similar to a comedy.”

While Macron sought to strike a constructive tone after meeting Monday with Putin for five hours in Moscow, little optimism emerged from Truss’ visit.

“I am honestly disappointed that we’re having the conversation of a mute person with a deaf person,” Lavrov said. “It’s as though we are hearing each other but not listening.”

Russia has made a series of demands of the West, including scaling back the NATO military presence in Eastern Europe to 1990s levels, and guaranteeing that Ukraine could never join NATO. The United States has called those demands “non-starters’’ and instead offered a series of proposals aimed at arms control.

Despite the apparent impasse, Western diplomatic efforts are continuing.

In Berlin, Chancellor Olaf Scholz of Germany met with the leaders of Estonia, Latvia and Lithuania, which all border Russia. The three Baltic nations welcomed Germany’s recent commitment to send an additional 350 troops to the German-led NATO mission in Lithuania. But they expressed frustration with Berlin’s decision not to supply defensive weapons to Ukraine and hinted that as a key NATO ally, Berlin should shore up its military spending.

Ben Wallace, the British defence minister, is expected to visit Moscow Friday to meet with his Russian counterpart. And next week, Scholz is due in Moscow for talks with Putin.

Gen. Mark Milley, chair of the Joint Chiefs of Staff, called his Belarusian counterpart, Maj Gen Viktor Gulevich, according to Belarus. The two discussed “regional security related issues of concern,” the Pentagon said, aiming to “reduce chances of miscalculation.’’

Truss insisted that the facts of the Russian troop buildup spoke for themselves. Her direct language was evidence of the relatively hard line that Britain has struck in the current crisis — alleging Russian plans for a coup in Ukraine, for example, and providing Ukraine with antitank weaponry.

“There is no doubt that the stationing of over 100,000 troops is directly put in place to threaten Ukraine,” said Truss, who was making the first visit to Moscow by a British foreign secretary in more than four years. “If Russia is serious about diplomacy, they need to move those troops.”

Britain’s prime minister, Boris Johnson, said during a visit to NATO headquarters in Brussels Thursday that he did not think Russia had made a decision on whether to launch an invasion. “But that doesn’t mean it is impossible that something absolutely disastrous could happen very soon indeed,” Johnson said.

Putin has kept the world guessing at his intentions, signalling that he is open to continued negotiations over his demands for a reshaping of Europe’s security architecture while hinting at the prospect of an all-out war with the West.

But Lavrov said that any Russian threats to Ukraine were pure fiction — a denial-of-reality approach that echoed Russia’s refusals to acknowledge its military backing for separatists in eastern Ukraine or its interference in the 2016 American elections. Lavrov even professed that Russia was so concerned about Western embassies drawing down their personnel in Kyiv, the Ukrainian capital, that Russia was planning to do so as well.

“We’ve started to think that maybe the Anglo-Saxons are preparing something,” Lavrov said, standing next to Truss. “If they are evacuating their employees, we will probably also recommend that nonessential personnel of our diplomatic establishments temporarily go home.”

Lavrov added that he had heard nothing from Truss that British officials had not already said in public.

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