As pressure mounts for the U.S. and its European allies to take swift action to deter Russian escalation, the coming action against Ukrainian individuals rather than the Russian government underscores some of the administration’s interest in exhausting diplomatic avenues with Moscow, officials said. The U.S. and its allies hope for a diplomatic breakthrough after four rounds of talks last week failed to narrow the gap between Moscow and Western nations.

The pending sanctions, which will freeze the assets of at least four individuals acting on behalf of Russia, could be announced as early as Thursday. They would be the latest in a string of actions under an executive order signed by President Biden last April that aim to punish individuals associated with Russia’s foreign aggression.

The State Department and Treasury Department declined to comment.

“We have been taking every effort to bring to light pro-Kremlin disinformation efforts and undermine Russia’s ongoing destabilization efforts in Ukraine,” a U.S. official said. “Russia is laying the groundwork to have the option of fabricating a pretext for invasion, including through sabotage activities and information and influence operations.”

Rachel Ziemba,

an adjunct senior fellow at the Center for a New American Security, said the move is a way to “signal concerns about lack of progress from diplomacy, while also trying to keep cohesion.”

“The U.S. administration is looking to thread the needle via targeting Ukrainian-based pro-Russian officials while still seeking to maintain cohesion on a broader, if shrinking, package,” she added.

U.S. officials haven’t identified the individuals whom the sanctions would target. Since 2014, Moscow has fomented separatist conflict in the country’s east, relying in large part on friendly Russian-speaking Ukrainians who have taken up arms against Kyiv government forces. Ukraine has also accused the Kremlin of using its vast network of agents in Ukraine to disrupt the peace and foment division.

In recent months, Moscow has deployed more than 100,000 troops to the border regions, prompting fears it plans to invade its neighbor or is generating a crisis to extract security concessions from the West. Russia also has been moving tanks, infantry fighting vehicles, rocket launchers and other military equipment westward from their bases in its Far East, according to U.S. officials and social-media reports.

The U.S. has pressed Russia to de-escalate the situation by withdrawing troops from the border region. Russia has said it has the right to move forces about on its own territory and denied it intends to invade Ukraine. But it has demanded concessions from North Atlantic Treaty Organization that would effectively rewrite the post-World War II security establishment on the European continent.

On Wednesday, Mr. Blinken will meet Ukrainian President

Volodymyr Zelensky

and Foreign Minister

Dmytro Kuleba

in Kyiv, demonstrating the U.S. commitment to Ukraine’s sovereignty. Mr. Blinken also will discuss with U.S. diplomats and their families the State Department’s contingency planning, should Russia “choose to escalate further,” a senior State Department official said. The security situation in Ukraine is severely deteriorating, the official said, noting the U.S. has warned Americans not to travel there.

The next day, Mr. Blinken will travel to Berlin to meet Germany’s new foreign minister, Annalena Baerbock, to discuss allies’ preparations to impose “massive consequences and severe economic costs” on Russia if it invades Ukraine. The U.S. is weighing a set of leveraged financial sanctions and export controls, while likely avoiding the most crippling energy and financial sanctions, U.S. officials have said.

Despite repeated assurances from the U.S. and its European allies that Ukraine’s fate wouldn’t be discussed without Kyiv at the table, President Zelensky was sidelined in the latest talks. Of the four rounds of talks last week, Ukrainian officials were present at the table only on Thursday, in the Organization for Security and Cooperation in Europe. Current and former advisers to Mr. Zelensky say Moscow won’t deal with the Ukrainian president because he refuses to submit to Moscow’s demands as the price of peace.

Mr. Blinken’s visit to Kyiv follows visits by Ms. Baerbock of Germany and Canadian Foreign Minister

Mélanie Joly.

And earlier this week, a group of U.S. senators met Mr. Zelensky and other top officials in Kyiv. The delegation, led by Sen. Rob Portman (R., Ohio), discussed U.S. defense assistance to Ukraine, among other topics.

Mr. Blinken spoke with Russian Foreign Minister Sergei Lavrov on Tuesday and the two are scheduled to meet Friday in Geneva, a sign that hopes of a diplomatic solution to the Ukraine standoff aren’t dead, a senior State Department official said.

The White House on Tuesday characterized the escalating security situation along Ukraine’s border as “extremely dangerous.”

“We’re now at a stage where Russia could at any point launch an attack in Ukraine,” White House press secretary

Jen Psaki

said. She added that no option is off the table and warned of “severe consequences” if Russia further invades Ukraine.

A senior administration official also expressed concern on Tuesday over Russia’s latest military exercises in Belarus, warning the movements could be a guise for military operations aimed at Ukraine.

Mr. Lavrov said Tuesday that he is expecting a response to demands presented late last year to the U.S. and NATO, which called for fixed legal guarantees to ensure Russia’s security, the Foreign Ministry said following his call with Mr. Blinken.

“We reaffirmed the imperative that Washington provide specific, article-by-article comments on the documents mentioned as soon as possible, on paper,” the statement said.

Russia wants NATO to forswear future expansion into Ukraine and other former Soviet countries, curb the alliance’s ties with Ukraine and former Soviet states and restrict military deployments on the territory of the alliance’s Eastern European members.

The Biden administration has ruled out direct U.S. military intervention inside Ukraine, but Mr. Blinken is seeking European support for a significant sanctions package to be deployed if Ukraine is invaded. European countries have closer economic and financial ties to Moscow than the U.S. and thus would suffer more collateral damage from any sanctions, hindering agreement between the U.S. and Europe on a synchronized package of measures, European officials said.

—Ann M. Simmons in Moscow contributed to this article.

Write to Vivian Salama at vivian.salama@wsj.com and William Mauldin at william.mauldin@wsj.com