The existence of the message was disclosed because the Kremlin was funneling armaments, together with assault helicopters, to Russia’s border with japanese Ukraine for the following part of its two-month-old invasion of the nation.

Over the course of the struggle, the U.S. administration has offered more and more heavier weapons to the Ukrainians — together with 155-mm howitzers — because the battle has ramped up, and it introduced a brand new $800 million arms package deal this week.

Again in February, because the struggle started, the administration fearful such weaponry might unnecessarily provoke Russia. However after coming underneath stress from President Volodymyr Zelensky of Ukraine and members of Congress from each events, the administration has determined to offer a few of the sorts of heavy weapons it says Ukraine would require within the subsequent part of the struggle.

The Russian warnings have come because the invasion has met unexpectedly stiff Ukrainian resistance and has uncovered weaknesses in Russia’s standard armed forces.

President Vladimir V. Putin of Russia has put in a brand new command to supervise the Ukraine struggle and this previous week publicly urged for the primary time that Russia’s objectives have been restricted to securing the Donbas, the part of japanese Ukraine bordering Russia the place Moscow-backed separatists have been preventing for eight years.

Russia’s objectives when its navy invaded on Feb. 24 appeared way more bold, with plans to besiege and seize the capital, Kyiv, within the north, slicing off Mr. Zelensky’s authorities from the remainder of the previous Soviet republic, which Mr. Putin has stated he doesn’t even think about a rustic.

That technique backfired and Russian forces retreated final month. In addition they have didn’t utterly seize the strategic southeast port of Mariupol regardless of relentless bombardments which have turned that when bustling metropolis of 450,000 right into a wasteland of dying and struggle’s damaging horrors.

Pavlo Kyrylenko, the governor of the Donetsk area of Japanese Ukraine, instructed CNN on Friday that Ukrainian troops have been nonetheless answerable for Mariupol, however that town had been “wiped off the face of the earth by the Russian Federation, by those that won’t ever be capable to restore it.”

In what gave the impression to be one other navy embarrassment for Russia that it has sought to cowl up, a senior U.S. protection official stated Friday that Russia’s Black Sea flagship Moskva, a missile cruiser that sank Thursday, had been struck by two Ukrainian Neptune missiles, and never crippled by an unintentional hearth and explosion throughout a storm, because the Kremlin has asserted.

It was the primary American corroboration of Ukraine’s claims that its Neptune missiles — a newly deployed weapon with a 190-mile vary — had hit the ship, which was struck 65 miles south of the port of Odesa.

The lack of the Moskva was greater than only a humiliation, because it might now significantly impair any Kremlin plans for an amphibious assault on Ukraine’s southern coast. The loss additionally raised questions on Russian dominance of Ukraine’s airspace and the obvious lack of ability of the Moskva, a classy warship, to evade or intercept the Neptunes with its personal protection techniques.

The U.S. official stated that American intelligence assessments had indicated an unspecified variety of casualties, contradicting Russian claims that every one crew members had been safely evacuated.

The Russian diplomatic protest notice, known as a démarche, was despatched by way of regular channels, two administration officers stated, and was not signed by Mr. Putin or different senior Russian officers. But it surely was an indicator, one administration official stated, that the weapons despatched by the USA have been having an impact.

American officers stated the tone of the notice was in line with a collection of public Russian threats, together with to focus on deliveries of weapons as they moved throughout Ukrainian territory.

Officers stated the notice didn’t immediate any particular concern contained in the White Home. But it surely has touched off a broader dialogue contained in the Pentagon and intelligence companies about whether or not the “unpredictable penalties” might embody attempting to focus on or sabotage a few of the weapons shipments whereas nonetheless in NATO territory, earlier than they’re transferred to Ukrainians for the ultimate journey into the arms of Ukrainian troops. The supply of the protest notice was first reported by The Washington Submit.

The weapons President Biden approved this week for switch to the Ukrainians embody long-range artillery that’s suited to what American officers consider shall be a special model of battle within the open areas of the Donbas, the place Russian forces seem like massing for an assault in coming days.

Pentagon officers have been insistent within the run-up to the struggle that the USA present solely defensive weaponry that will keep away from escalation.

Jake Sullivan, the president’s nationwide safety adviser, described in an interview on the Washington Financial Membership on Thursday how he and Gen. Mark A. Milley, the chairman of the Joint Chiefs of Employees, had reviewed weapons requests. They went over every merchandise with their Ukrainian counterparts, speaking about what the USA had in its shares and what it might ship rapidly.

Stories by pro-Kremlin media have highlighted antitank techniques and different Western weapons utilized by Ukrainian forces, selling the concept Russia isn’t at struggle with Ukraine however with an American-led alliance looking for to destroy Russia. Mr. Biden and his aides have denied that, saying that they wished to keep away from direct battle with Russia and had no real interest in American-engineered regime change.

In Moscow, commentators have been more and more calling on Russia to strike Ukrainian roads and railroads to inhibit the weapons transfers. Whereas Russia has focused lots of Ukraine’s airports, the nation’s floor transportation community stays largely intact.

“The time has come to not communicate, however to assault,” Viktor Baranets, a navy columnist for Komsomolskaya Pravda, Russia’s greatest tabloid, stated on Friday. “Prepare echelons should be destroyed together with the railways.”

Russia’s concern might partly be over the accuracy Ukraine confirmed in hitting the Moskva, considered one of its most subtle warships.

The Russian démarche echoed the general public rhetoric of officers in Moscow, who’ve been warning for weeks that Western arms deliveries to Ukraine would lengthen the struggle and be met with a tricky response.

It got here as the extent of concern amongst Russian officers over the affect of Western arms has been rising, stated Andrei Kortunov, the director basic of the Russian Worldwide Affairs Council, a analysis group near the Kremlin.

“It appears the USA and the West generally are proper now testing the bounds of Russian tolerance in relation to weapons deliveries,” Mr. Kortunov stated. “It’s clear that these volumes are already so important that they will have an effect on the course of the hostilities, and that is elevating considerations.”

A Russian deputy overseas minister, Sergei A. Ryabkov, stated on Friday that Russia was “making it clear to the Individuals and different Westerners” that makes an attempt to hamper what Russia is asking its “particular navy operation” in Ukraine and improve Russian losses could be “curbed in a tricky method.”

He added that NATO autos carrying weapons throughout Ukrainian territory could be “considered by us as legit navy targets.” His feedback got here in an interview with Tass, the state-run information company.

NATO arms off weapons to the Ukrainians in ways in which search to keep away from having the alliance’s autos traverse Ukrainian soil. However Mr. Ryabkov’s feedback have heightened considerations about whether or not Russia would take the chance of placing inside NATO territory.

When Mr. Putin introduced his “particular navy operation” on Feb. 24, he stated that these “who could also be tempted to intervene” in Ukraine would face penalties as extreme “as you could have by no means seen in your total historical past.”

“Regardless of how the occasions unfold, we’re prepared,” Mr. Putin stated on the time. “All the required selections on this regard have been taken.”

However Russia has to date appeared cautious to not escalate the battle in a means that would draw NATO international locations extra instantly — as an illustration, not placing weapons convoys crossing into Ukraine from Poland.

“There are nonetheless fears concerning strikes which will hit the territory of NATO member international locations,” Mr. Kortunov stated. “One actually doesn’t need to create a pretext for some additional escalation.”

David E. Sanger and Helene Cooper reported from Washington, and Anton Troianovski from Istanbul. Reporting was contributed by Marc Santora from Krakow, Poland; Michael Schwirtz from Lviv, Ukraine; and Julian E. Barnes and Eric Schmitt from Washington.