As Russia continues to mass troops and military equipment near Ukraine's borders, including now in allied Belarus, the U.S. and European countries have become increasingly concerned the Kremlin may be preparing to launch an attack on Ukraine.
But Blinken will meet his Russian counterpart, Foreign Minister Sergei Lavrov, in Geneva on Friday, keeping the door to diplomacy open.
"This is an extremely dangerous situation. We're now at a stage where Russia could at any point launch an attack in Ukraine," White House press secretary Jen Psaki said Tuesday -- a sharp rise in the United States' rhetorical warnings that Russian lead Vladimir Putin may attack his neighbor.
Before sitting down with Lavrov, Blinken will meet Ukrainian President Volodymyr Zelenskiy and Foreign Minister Dmytro Kuleba in his second visit to Kyiv as secretary - one week after CIA Director Bill Burns visited - and travel to Berlin for a summit with his German, French, and British counterparts.
Months of Russian troop buildups and bellicose rhetoric led to a series of high-stakes diplomatic meetings last week. But the one-on-one U.S.-Russia talks, a summit between NATO and Moscow, and a meeting of the Organization for Security and Cooperation in Europe ended inconclusively.
Putin laid out his demands in two draft treaties last month, including that Ukraine be barred from joining NATO and that the Western military alliance pull its troops out of Eastern European member states. But for weeks, the U.S. and NATO have called those nonstarters, instead offering to negotiate on other issues like arms control or military exercises and threatening massive sanctions if Russia attacks Ukraine.
Russia has denied that it plans to invade Ukraine, where its troops have led eastern forces in a war against the government for eight years now and continue to occupy the peninsula Crimea. It has warned that if its demands aren't met, it will respond with "military technical" measures.
Rather than tensions defusing, the threat of conflict seems to be rising, engineered by Russian moves. The Kremlin has begun moving troops into Belarus, Ukraine's neighbor to the north, for military exercises next month, including troops from its far east, Russia's Defense Ministry confirmed Tuesday, saying the exercises were designed to prepare Russian and Belarusian forces to "thwart and repel a foreign aggression."
"This is neither an exercise nor normal troop movement," the senior State Department official told reporters. "It is a show of strength designed to cause or give false pretext for a crisis as Russia plans for a possible invasion."
A second senior State Department official went further later on Tuesday, calling into question whether the Belarusian government of strongman Alexander Lukashenko is really in charge and accusing the Kremlin of "preying" on his vulnerabilities with this "concerning" troop deployment.
"Over time, Lukashenka has relied more and more on Russia for all kinds of support, and we know that Putin doesn't give that support for free. ... There is no escaping that having dedicated his 27 years in office to claiming to be the guarantor of Belarus's sovereignty and independence, Lukashenka has increasingly shown that he will trade it all in order to stay in power," the senior official said.
The bold accusation seems to be a sign of deep U.S. concern that Putin is making another power move here - this time to deepen his influence in Belarus.
But the U.S. clearly sees it as a way for Moscow to more easily attack Ukraine, too - with Kyiv hundreds of miles closer to Belarus's borders than to Ukraine's eastern border with Russia. The deployment gives "increased capability for Russia to launch this attack - increased opportunity, increased avenues, increased routes" against Ukraine, the second senior State Department official said.
Last Friday, the White House also said the U.S. had intelligence that Russia had positioned operatives trained in urban warfare and explosives for a possible "false-flag" operation that could also been used as pretext for an invasion - something the Kremlin denied as "complete disinformation."
Blinken and Lavrov spoke Tuesday and agreed to meet Friday in Geneva, where U.S. and Russian delegations met last week. Their meeting will be another attempt to deescalate tensions, but it's unclear what new ground there is to tread.
"It is still too early to tell if the Russian government is genuinely interested in diplomacy, if it is prepared to negotiate seriously in good faith, or whether it will use discussions as a pretext to claim that diplomacy didn't address Moscow's interest. I just can't judge that now, but I do understand the desire on our side to test that hypothesis," the first senior State Department official said.
Before traveling to Switzerland, Blinken will be hosted by Zelenskiy in Kyiv, days after a bipartisan delegation of U.S. lawmakers visited and vowed continued U.S. support too, including arms.
"As we speak there are additional U.S. supplies that are being sent to Ukraine to make sure that they have what they need to fight back," Sen. Chris Murphy, D-Conn., told ABC News.
Blinken's visit comes on the heels of CIA Director Burns's last week, a senior U.S. official confirmed to ABC News. Burns also met with Zelenskiy and with his intelligence counterparts to discuss current assessments of the risk to Ukraine, the official said.
In between Kyiv and Geneva, Blinken will meet German Foreign Minister Annalena Baerbock for the second time this month, with the new German government critical to the strength of any potential sanctions if Russia invades. Blinken and Baerbock will also meet their French and British counterparts in a show of diplomatic solidarity.
There had been some signs of cracks in that unity, however, especially over the Nord Stream 2 pipeline. The project would bring natural gas from Russia to Germany, sidestepping Ukraine and removing a key source of revenue for Kyiv, which has pressed the U.S. to sanction the German company constructing it. But Biden has refused to do so, saying relations with Germany would suffer.
Amid intense international pressure, Germany's new chancellor Olaf Scholz indicated Tuesday that he would be prepared to halt the pipeline if Russia attacks Ukraine - another signal of the costs Moscow would face if it moved ahead.
"If Russia does launch an attack on a sovereign country that borders NATO countries, it is likely that NATO will significantly increase its military activities, funding, and even membership - everything Russia claims to be trying to avoid," said Mick Mulroy, former deputy secretary of Defense and a retired CIA paramilitary officer.
That could include Nord Stream 2's end and increased U.S. arms and training to Ukraine, too - with Mulroy adding, "Russia could end up in a prolonged counterinsurgency campaign in Ukraine, which they will soon regret."
ABC News's Patrick Reevell contributed to this report from Kyiv and Cindy Smith from Washington.