Biden Seeks to Reassure Ukraine, Vowing a Strong Response to Russia and Transferring Weapons

Mr. Biden’s comments came one day after he sparked criticism, both domestically and in Europe, when he suggested a “minor incursion” by Russia would be met with less than the punishing economic measures his administration has promised for weeks.

Ukraine, already unnerved by the presence of almost 100,000 Russian troops near its borders, was shaken by the comments, and several officials spoke out, saying that any suggestion of a weaker response would only encourage Mr. Putin.

Military force locations:

Military force locations:

Military force locations:

“Speaking of minor and full incursions or full invasion, you cannot be half-aggressive. You’re either aggressive or you’re not aggressive,” Ukrainian Foreign Minister

Dmytro Kuleba

said in an interview with The Wall Street Journal. “We should not give Putin the slightest chance to play with quasi-aggression or small incursion operations.”

Beyond Mr. Biden’s remarks on Thursday, the administration permitted the Baltic nations of Estonia, Lithuania and Latvia, hard on Russia’s border, to send Ukraine U.S.-made Javelin antitank weapons and Stinger air-defense systems, U.S. officials said.

Five Russian-made Mi-17 transport helicopters will also be transferred to Ukraine, the officials said. The helicopters had been intended for Afghanistan’s military and were being repaired in Ukraine when the U.S.-backed Afghan government collapsed.

U.S. Secretary of State

Antony Blinken,

who traveled to Kyiv earlier this week, met Thursday in Berlin with the German chancellor as well as with the foreign ministers of Germany and France and a senior United Kingdom official.

Mr. Blinken is due to meet Russian Foreign Minister

Sergei Lavrov

on Friday in Geneva. In his messaging, Mr. Blinken sought to project unity among the allies.

“If any Russian military forces move across the Ukrainian border and commit new acts of aggression against Ukraine, that will be met with a swift, severe, united response from the United States and our allies and partners,” Mr. Blinken said after his meeting with the German, French and U.K. ministers.

Ukrainian officials are touchy in part because their analysis is that a large-scale attack isn’t Russia’s probable course. Stiff Ukrainian resistance to a direct assault and pressure from the West would act as a deterrent, the officials said. Instead, they said, the Kremlin would probably deploy more covert measures to destabilize its neighbor and remove its leadership.

Mr. Biden didn’t directly address the Ukrainian criticism but noted that the Ukrainian foreign minister had voiced confidence in U.S. support. “And he has the right to be,” Mr. Biden said.

“Let there be no doubt at all that if Putin makes this choice, Russia will pay a heavy price,” he said.

On Wednesday, at a news conference marking his first year in office Wednesday, Mr. Biden said Russia would be held accountable if it invaded Ukraine, adding, “It depends on what it does. It’s one thing if it’s a minor incursion, and then we end up having a fight about what to do and not do.”

He said that if Russia invades Ukraine, “it is going to be a disaster,” and the U.S. and its allies would respond with measures including economic sanctions.

The White House said in a statement following Mr. Biden’s remarks that if any Russian military forces move across the Ukrainian border, it would be regarded as “a renewed invasion” and met with swift consequences from the U.S. and its allies.

Ukrainian leaders are trying to reassure citizens and stave off panic as the number of Russian troops around the country continues to swell. Ukrainian President

Volodymyr Zelensky,

in a televised address Wednesday, noted that the country had lived under the threat of war since 2014, when Russia first invaded.

“The risks have been present for more than a day, and they haven’t grown,” Mr. Zelensky said. “The hype around them has grown.”

Ukrainian officials are urging Western leaders not to play down apparently less-lethal aggression by Moscow, because attacks are likely to begin in more covert ways—with a flurry of cyberattacks, disinformation and provocations designed to destabilize the country and manufacture a pretext for invasion.

Oleksiy Danilov, secretary of Ukraine’s National Security and Defense Council, said in an interview that a military invasion would be very costly for Russia, given the size of Ukraine’s army, the population’s will to fight and pressure from the West. More likely, he said, Russia would seek, at least in the short term, to intensify a campaign of cyberattacks, provocations, disinformation and economic pressure.

“It will be very difficult for them to achieve their aims by military means. I think, impossible,” said Mr. Danilov. “They have a multifaceted plan to destabilize the domestic situation on the territory of our country. That’s the number one task for them.”

The threat assessment presented by Mr. Danilov underscores the difficulty for Ukrainian and Western officials trying to gauge Mr. Putin’s plans.

The Kremlin has denied it is planning an invasion, but Mr. Putin has repeatedly indicated he wants to pull Ukraine, which aims to join the North Atlantic Treaty Organization and the European Union, back under Russia’s control.

In 2014, Russia seized Crimea and tried to foment separatist uprisings across Ukraine’s east and south, according to Western and Ukrainian officials. Those rebellions gained a foothold only in two eastern regions with the help of Russian fighters, equipment and, eventually, a covert military invasion.

Today, Ukraine’s army is considerably stronger and better equipped than in 2014, with modern weaponry, including Javelin antitank missiles provided by the U.S. and attack drones from Turkey. Still, Russia’s military is significantly more potent, with a powerful air force and missiles that Ukraine would struggle to counter.

Mr. Putin’s options now could include attempting to invade and occupy parts of Ukraine, using a rapid assault to force Kyiv to negotiate, or seeking to pressure the West into compromises with the threat of action, current and former Ukrainian officials said.

Mr. Danilov said Russia, along with Belarus, was behind a cyberattack last week. The U.S. said Russia had deployed a group of operatives to launch a false-flag operation in eastern Ukraine. Mr. Zelensky accused Russia late last year of plotting a coup against him. Russia has denied involvement.

—Michael R. Gordon in Washington and William Mauldin in Berlin contributed to this article.

Write to Vivian Salama at vivian.salama@wsj.com, James Marson at james.marson@wsj.com and Alex Leary at alex.leary@wsj.com