The Pentagon said on Wednesday it would send an additional $1.1 billion in long-term military aid to Ukraine, including 18 High Mobility Artillery Rocket System launchers, or HIMARS, one of the most vaunted weapons of the seven-month war with Russia.

But unlike the 16 HIMARS the military rushed to Ukraine from its existing stockpiles over the summer, these new weapons will be ordered from the manufacturer, Lockheed Martin, and will take “a few years” to deliver, a senior Defense Department official told reporters.

Shifting the source of Ukrainian military supplies from the Pentagon’s own stockpile, which is large but not limitless, to items newly manufactured by the defense industry indicates that the White House and military leaders are transitioning to a sustainable model Kyiv can depend on for an open-ended war with Russia.

Privately, American commanders have also voiced concern that if the United States sends more HIMARS vehicles immediately, the Ukrainians will burn through the rocket ammunition provided by the Pentagon too quickly, potentially jeopardizing American military readiness in coming months.

The promise of new military aid comes at a critical time in the war, when Ukraine has the momentum on the battlefield, and has retaken vast stretches of land in the east and is pressing entrenched Russian forces in the south.

The Russian president, Vladimir V. Putin, is mobilizing up to 300,000 reservists in an attempt to shore up his forces, and Ukrainian commanders are pushing to try to take back as much territory as they can before the winter freeze forces both sides to slow their operations and dig in. The HIMARs systems have proven effective at cutting Russian supply lines, destroying ammunition depots, bridges, rail links, and troop concentrations far beyond the lines.

Asked why the Pentagon didn’t just send more of the advanced rocket launchers from its own inventories — as President Volodymyr Zelensky of Ukraine has repeatedly requested — the senior Defense Department official sidestepped the question, saying the future delivery was to ensure Ukraine “will have what it needs for the long haul to deter future threats.”

Pentagon officials have said for weeks that with the American HIMARS and 10 similar rocket systems already delivered to the battlefield — 26 rocket-launchers in all — Ukraine has enough of the weapons to attack the Russian targets it wants. Indeed, the satellite-guided rockets fired by HIMARS have struck more than 400 Russian ammunition depots, command posts and radars.

The new shipment announced on Wednesday also includes 150 Humvees, 150 vehicles for towing artillery, radars, counter-drone systems and body armor, which the senior Pentagon official said would be delivered from manufacturers in the next six to 24 months. That brings to $16.2 billion in total military aid that the United States has committed to Ukraine since the war started in February.

The $1.1 billion in new equipment will be paid for by the Ukraine Security Assistance Initiative, a congressionally approved fund that allows Ukrainian leaders to purchase military goods directly from the defense industry.

At the same virtual briefing for reporters on Wednesday, a senior U.S. military official said the first “small group” of Russians from the 300,000 conscripts ordered mobilized had arrived in Ukraine. The official did not provide details on how many new conscripts had been sent to the battlefield or where they were located.

But the official, who like the senior Pentagon official spoke on condition of anonymity to discuss operational matters, expressed skepticism that the Kremlin could properly mobilize, train and equip anywhere near that total number of new troops.

“Just the mechanics of outfitting that size of a force is very difficult,” the senior U.S. military official said.

The European Union proposes a fresh round of sanctions against the Kremlin over ‘sham’ referendums.

The European Union put forward a series of new sanctions on Wednesday aimed at punishing Russia for escalating the Ukraine war by drafting at least 300,000 men into its army, threatening the use of nuclear arms and holding discredited referendums in occupied territories widely seen as a prelude to annexation.

The draft measures were proposed by the European Commission, the bloc’s executive arm, and they include an oil price cap, trade restrictions, and blacklisting several individuals responsible for what the officials called “sham” referendums.

To put the sanctions in place, all member nations would need to greenlight the package, and Hungary is expected to be the main obstacle. The European Union has already imposed seven rounds of severe financial sanctions against Russia since it invaded Ukraine, and Hungary emerged as the key spoiler to the bloc’s joint response to Moscow.

“Last week, Russia escalated the invasion of Ukraine to a whole new level” through the referendums in occupied territories, military mobilization and nuclear threats, Ursula von der Leyen, the bloc’s top official, told reporters on Wednesday. “We’re determined to make the Kremlin pay for this further escalation.”

Josep Borrell Fontelles, the European Union’s top diplomat, said the bloc condemned “in the strongest possible terms the illegal sham ‘referenda’,” calling them a clear breach of international law and Russia’s international obligations. “All those involved in organizing these illegal sham ‘referenda’ as well as those responsible for other violations of international law in Ukraine will be held accountable,” he added.

An import ban on Russian products included in the proposal would cost Moscow seven billion euros, Ms. von der Leyen said, while a prohibition of exporting European products, such as aviation items or chemical substances to Russia, would weaken “the Kremlin’s military complex.”

The proposal also lays out “a legal basis” for a cap on the price of oil, though Ms. von der Leyen did not provide further details. Earlier this year, the bloc reached an agreement on banning Russian seaborne oil imports, which make up a great majority of the fuel shipments coming from Moscow into the bloc.

The Commission also wants to ban European nationals from sitting on governing bodies of Russian state-owned companies, so that Moscow could no longer profit from “European knowledge and expertise.” A number of former European officials served as board members of large Russian companies, the most prominent example being the former German chancellor Gerhard Schröder, who was paid almost $1 million a year by Russian-controlled energy companies.

But foreign policy is traditionally the realm of national governments, and the Commission’s proposal requires the approval of all member nations. Hungary’s leader Viktor Orban has repeatedly said he would veto further energy sanctions.

Speaking to the Hungarian parliament on Monday, Mr. Orban said the sanctions adopted by Brussels were hurting Europe more than Russia.

“We can safely say that as a result of the sanctions, European people have become poorer while Russia has not fallen to its knees,” he said. “This weapon has backfired: with the sanctions Europe has shot itself in the foot.”