RUTHFULLY YOURS

In response, Ukraine said Tuesday it had put its own forces on alert and was reinforcing units in eastern Ukraine and on the border with the Russian-occupied peninsula of Crimea.

While Mr. Biden has wrestled with Kremlin machinations such as a massive suspected Russian hack of U.S. government computer systems and the assessment by U.S. intelligence that Moscow attempted to interfere in the 2020 election, the situation in Ukraine is the first involving movements of Russian troops. Russia has denied meddling in the election and denied responsibility for the hack.

In Washington, a State Department spokesman said the department was discussing the situation with NATO allies.

“We are concerned by recent escalations of Russian aggression in eastern Ukraine, including violations of the July 2020 cease-fire that led to the deaths of four Ukrainian soldiers on March 26 and the wounding of two others,” a State Department spokesman said.

The Pentagon said it was monitoring the situation and that Chairman of the Joint Chiefs of Staff Army Gen. Mark Milley spoke with both his Russian and Ukrainian counterparts.

While analysts say Russia hasn’t summoned enough troops for an outright invasion of eastern Ukraine, analysts say Moscow could be looking to provoke a flare-up in fighting and test the depth of President Biden’s support for Ukraine.

In the recent troop mobilization, Russia’s defense ministry announced a series of exercises less than 70 miles from the Ukrainian border in recent weeks, though further details of the buildup are unclear.

In a speech before Ukraine’s parliament earlier this week, Ukraine’s military commander-in-chief, Lt. Gen. Ruslan Khomchak, said the exercises were a guise to draw tactical groups from around Russia to Ukraine’s borders, and that troops have remained after the end of exercises.

The troop deployments recall moves after Russia’s annexation of Crimea in 2014, when Russian President Vladimir Putin rotated military units to the border with Ukraine, said Mikhail Barabanov, a military expert at the independent Moscow-based Center for Analysis of Strategies and Technologies,

“At the moment there are several battalions of tactical groups from other military districts, similar to how [reinforcements of the border] were made in 2014 and 2015,” he said.

Following the 2014 conflict, a handful of regiments were transferred from deep inside the country to the border, where they were established on a permanent basis as a first line of support for pro-Russian separatists in the Ukrainian breakaway territories in Donetsk and Luhansk provinces, he said.

Current troop movements, he said, may be aimed at boosting the numbers and capabilities of those units.

A mission from the Organization for Security and Cooperation in Europe, tasked with monitoring violence along the front line, said in recent days that observers had seen infantry fighting vehicles and antitank missiles on separatist territory. Footage on a Russian channel on the social media site Telegram showed a long column of Russian mechanized howitzers being carried on trucks toward Crimea, across a 12-mile bridge that Moscow built connecting the peninsula to the Russian mainland after the annexation.

Moscow wants to test the Biden administration’s commitment to Ukraine, but it is also frustrated with its own failure to achieve its goals there, said James Sherr, a senior fellow at the Estonian Foreign Policy Institute at the International Centre for Defense and Security in Tallinn, Estonia, that supports the country’s integration in the West.

In February, the government of Ukrainian President Volodymyr Zelensky cracked down on a pro-Russian politician in Ukraine, Viktor Medvedchuk, who is a close friend of Mr. Putin’s, closing three TV stations under his control and then freezing his assets and preventing him from doing business in the country. In ordering the closure of TV stations, Mr. Zelensky said they were financed by “the aggressor country”—a reference to Russia.