Satellite images show the growing build-up of Ukraine in Russia

Other Russian military units in the Crimean peninsula include airborne troops, self-propelled guns and armored units, attack helicopters, smoke generators, reconnaissance drones, jamming equipment and a military hospital, the photos show.

Those armed forces and the deployment of Su-34, Su-30, Su-27, Su-25 and Su-24 aircraft elsewhere in the region, which are also depicted in the photos, have Moscow’s political influence reinforced to Ukraine, current and former officials say.

“They appropriately deployed the various elements of the Air Force that would be needed to establish air superiority over the battlefield and directly support the ground forces,” said Philip Breedlove, a retired United States Air Force general who served as the top military commander. of NATO when Russian forces seized Crimea in 2014 and intervened in eastern Ukraine.

General Breedlove said the photos indicated that the Russian units were not ready to strike immediately, but said Moscow has multiple options for taking military action.

William Burns, director of the Central Intelligence Agency, gave a similar assessment to Congress last week, noting that the Russian deployment may have been intended to intimidate the Ukrainian government and send a message to the Biden government.

“That build has reached the point where, you know, it could also be the basis for a limited military incursion,” Mr. Burns told the Senate Intelligence Committee. “So it’s something that not only the United States but our allies must take very seriously.”

Biden government officials have prepared options to provide lethal and non-lethal military assistance to Ukraine in the event of a Russian attack. The options include anti-tank, anti-ship and anti-aircraft systems, according to a person familiar with the deliberations, although they have not yet been submitted to President Biden for decision. The government is also considering more economic sanctions against Russia, government officials say.

Russian Defense Minister Sergei Shoigu said last week that the country was conducting exercises in response to measures by the North Atlantic Treaty Organization that “threaten Russia” and accused the Ukrainian authorities of stirring tensions.

The satellite photos were taken between March 27 and April 16 by Maxar Technologies

a commercial satellite and image editing company that provides comprehensive images to the US and other Western governments. Dan Jablonsky, the company’s chief executive, said it was making the unclassified photos public due to a commitment to transparency, but that the US government had not requested this.

“I think it removes some of the uncertainty and doubt about what is really happening in a fairly critical region of the world,” said Mr Jablonsky.

US officials estimate that there are currently as many as 80,000 Russians in Crimea and near Ukraine. That’s nearly double the Russian force deployed there about four weeks ago, officials said. Josep Borrell, head of the European Union’s foreign policy, estimated the number at more than 100,000, which he said would be greater than the force the Russians used when they conquered Crimea in 2014 and sent troops to eastern Ukraine.

According to a US military official, the Russian force currently comprises 48 tactical battalion groups, each of which consists of hundreds of soldiers and officers. However, US intelligence has not yet discovered all the logistical capabilities and support units that would generally be used for a significant attack across the Ukraine border, including ammunition supplies and deployable hospitals, the official said.

Su-34 planes at the Morozovsk base east of Ukraine had been relocated to the flight line, the satellite photos show, a move indicating a higher state of alert.

“This is not a demonstration. It is a preparation for a major offensive, ”said Phillip Karber, president of the Potomac Foundation, an American think tank that has traveled extensively to the military front in Ukraine. “I don’t predict an attack, but within two weeks it will be an option at the discretion of the Russians.”

Other experts say Russian President Vladimir Putin may be trying to pressure Ukraine to resume water supplies to Crimea, which Kiev authorities cut off after the Kremlin annexed the peninsula.

“We cannot rule out the possibility that this build-up may be a coercive force used by Putin to induce Ukraine to open the North Crimean water channel,” said Glen Howard, president of the Jamestown Foundation, a conservative research center. “It’s a tremendous amount of military capability, and we don’t know in which direction the Russians will go.”

In Ukraine, Russian troop build-up has left many guessing as to Mr Putin’s intentions, over seven years in a conflict that claimed more than 14,000 lives.

“In a few weeks, they will be close to enough combat readiness to continue a military escalation. According to our estimates, their combined military force will reach more than 120,000 troops by then, ”Ukrainian Foreign Minister Dmytro Kuleba said in written remarks to the Journal. “We don’t know if Putin will decide to attack, but he will certainly be willing to do so.”

Oleg Zhdanov, a reserve colonel in the Ukrainian military and military analyst, said that the fact that much of the build-up took place in the open air and recorded on social media was a sign that Moscow’s main goal was political. “Putin is using it to spread panic,” said Mr. Zhdanov.

The situation can be somewhat changeable. The satellite photos show that a squadron of ground attack Su-25 “Frogfoot” aircraft and a pair of electronic warplanes observed in Maxar satellite images at an air base in Astrakhan, Russia in mid-April, took off for another airfield by April 16. On Sunday, Russian news agency TASS said Su-25s had arrived in Crimea.

Mr Biden, speaking with Mr Putin last week, has called on Russia to ease tensions with Ukraine. Mr Biden announced new sanctions against Moscow last week over election interference and SolarWinds’ cyberattack. Moscow has denied involvement in the hack, and Russian officials have repeatedly denied interfering in the US elections.

Mr Biden said he was not keen to escalate but was willing to take firm action if needed.

National security adviser Jake Sullivan spoke to his Russian counterpart, Nikolai Patrushev on Monday. The statements made by the US and Russia on the talk noted that the two officials had discussed prospects for a summit meeting between Mr Biden and Mr Putin later this year. Neither statement specifically mentioned the Russian military build-up in Crimea and near Ukraine.

—Gordon Lubold in Washington and James Marson in Brussels contributed to this article.

Write to Michael R. Gordon at [email protected] and Georgi Kantchev at [email protected]