U.S. Wants to See Russia Weakened, Says Defense Secretary Lloyd Austin After Ukraine Visit

In an attempt to stem the flow of heavy weapons from the U.S. and other allies to the front lines in Ukraine, Russia on Monday hit several Ukrainian railway hubs with missile strikes, severely disrupting rail traffic. Meanwhile, large fires broke out at fuel-storage facilities in the Russian region of Bryansk, some 60 miles from the border with Ukraine, as well as at a nearby military fuel depot, Russian state media said.

Russian authorities said they were investigating the fires at the facilities, which Russian state media said together contained around 15,000 tons of fuel. The blazes erupted less than a month after Russia said Ukrainian helicopters launched strikes that caused a fire at an oil depot in Russia’s Belgorod region, also bordering Ukraine. Russian state media aired security-camera footage on Monday that appeared to show a large explosion followed by a fire.

Bryansk, Belgorod and Kursk, another region of Russia bordering Ukraine, have extended a state of alert they rolled out earlier this month, citing “possible provocations” from Ukraine. Authorities in Kursk said Monday that Russian air-defense forces had shot down two Ukrainian drones in the village of Borovskoye. There were no casualties or damage, they said. Meanwhile, Russian state media reported that a series of explosions rocked the building of the Ministry of State Security of Transnistria, a breakaway region in Moldova, which also borders Ukraine. Ukraine hasn’t claimed responsibility for any of the attacks.

The Russian missile strikes hit rail infrastructure in the central Ukrainian region of Rivne, local officials said. They followed other missile attacks late Sunday in Poltava that struck an electricity plant and a fuel refinery. The governor of Ukraine’s central province of Vinnytsia said early Monday that Russian missile attacks had hit critical infrastructure in the region and that there were people dead and injured, though he provided no details.

The strikes came hours after Messrs. Blinken and Austin told Mr. Zelensky that Washington would reopen its embassy in Kyiv and provide Ukraine with $322 million in foreign military assistance to allow Kyiv to buy needed weapons. Russia’s ambassador to the U.S.,

Anatoly Antonov,

demanded in a diplomatic note that Washington stop supplying weapons to Ukraine, Russian news agency RIA reported Monday.

“We believe that they can win if they have the right equipment, the right support,” Mr. Austin said, adding of Mr. Zelensky: “While he’s grateful for all the things we’re doing, he’s also focused on what he thinks he’ll need next in order to be successful.” Besides artillery, Ukraine has expressed an interest in getting more tanks, he said.

Mr. Zelensky said the $3.4 billion in defense support provided by the U.S. so far has been the biggest contribution to Ukraine’s defense efforts, adding that he had also discussed sanctions on Russia, financial support for Ukraine and security guarantees with the secretaries.

“I would like to thank President Biden personally and on behalf of the entire Ukrainian people for his leadership in supporting Ukraine, for his personal clear position,” he said on his website.

The White House said Monday that Mr. Biden planned to nominate

Bridget Brink,

the current U.S. ambassador to Slovakia, as ambassador to Ukraine. The position has been vacant since the last Senate-confirmed ambassador to the country,

Marie Yovanovitch,

was ousted by then-President

Donald Trump

in 2019.

Messrs. Austin and Blinken hailed Ukraine’s success in fending off Russia’s initial attack on Kyiv and maintaining its sovereignty. A senior State Department official briefed reporters on the flight out of Poland about many aspects of Ukraine’s military campaign that were discussed with Mr. Zelensky, including Russia’s depleted forces and inability to devote many more resources to the war without compromising its stance against the North Atlantic Treaty Organization and even Finland, which could join the alliance.

Still, U.S. officials said they recognized that Russian President

Vladimir Putin

could choose to escalate the war, including possibly with weapons of mass destruction.

“I suspect that May is going to be very much in his mind in wanting to show something, so we fully anticipate that he’s going to press the accelerator the best he can,” the senior official said. “We’re trying to be prepared for everything.”

Having struck Odessa in recent days, the senior official said, Mr. Putin is “looking at the entire expanse of the Black Sea coastline.”

The official declined to comment on the explosions in Bryansk in the absence of sufficient information or analysis.

At a briefing in Poland after his return from Kyiv, Mr. Blinken said he spoke to United Nations Secretary-General

António Guterres

on Friday and that the U.N. chief, set to visit Moscow and Kyiv this week, would send a “clear, direct message” on behalf of most of the world that Russia should agree to a cease-fire, provide needed aid to civilians and stop the war.

Mr. Guterres had appealed for a four-day truce during the Orthodox Holy Week to allow for the evacuation of civilians from front-line towns and the delivery of humanitarian aid.

The cease-fire proposal was rejected by Moscow, which said it was a ruse to allow Ukraine’s military to rest and regroup.

Senior U.S. military officers at a facility in Poland described an accelerating logistical network for supplying weapons and materiel to Ukraine, as well as a regional effort to increase troop levels and exercises with NATO members along the alliance’s eastern flank.

Seven 155-mm artillery pieces, along with their tow vehicles, are being processed through the facility, adding to the 18 howitzers the U.S. has already provided to Ukraine, a senior defense official said. Six dozen U.S. howitzers are being sent to Ukraine under a new aid package, and rounds of 155-mm artillery were visible on pallets at the Polish facility.

The focus on heavy artillery and armored vehicles comes as Russia removes some of its forces from around cities in northern Ukraine and focuses instead on the eastern Donbas region, in what is expected to be a high-stakes conflict on wide-open terrain.

Mr. Austin on Tuesday will join other defense ministers, including Ukraine’s

Oleksii Reznikov,

and NATO Secretary-General

Jens Stoltenberg

at a gathering at Ramstein Air Force Base in Germany. The topics to be discussed will include updating the representatives of more than 20 countries about the latest intelligence from the battlefield in Ukraine, security assistance to Kyiv and strengthening NATO’s defense-industrial base in the long term to support Ukraine’s defense, the defense official said.

One problem to be addressed at the gathering is Ukraine’s need for what NATO considers to be nonstandard ammunition and weapons systems, as well as discussions about whether the former Soviet republic could shift toward standard NATO equipment, the official said. For example, howitzers designed to fire 152-mm rounds can’t accommodate the 155-mm caliber.

The return of a U.S. diplomatic presence to Ukraine, which follows moves by the U.K., Italy, France and other countries, will help American and Ukrainian officials to coordinate aid and other efforts in person and to prepare for a future consular operation to address the needs of citizens of both countries, a State Department official said. The defense official declined to say whether U.S. Marines would help guard the embassy in Kyiv, saying the military would respond to the State Department’s needs.

Asked whether the increased U.S. focus on Ukraine risks increasing tensions with Russia, the State Department official said Washington has no plans to involve its troops in the conflict.

—Mauro Orru in Barcelona contributed to this article.

Write to William Mauldin at william.mauldin@wsj.com and Thomas Grove at thomas.grove@wsj.com