MOSCOW - A spokesman for President Vladimir Putin said Thursday there is “little optimism” about ending Russia’s confrontation with United States and NATO over Ukraine after the allies rejected Moscow’s key demands, but he opened the path for further high-level talks.

Dmitry Peskov, the Kremlin spokesman, said Putin has studied the proposals and that his response will be swift - raising the prospect of further dialogue even as more Western military aid arrives in Ukraine amid fears that Russia could push across the border at any time.

“The president is consulting members of the leadership and Security Council members,” Peskov said in a telephone news conference. He added that Washington and NATO were “loud and clear” about their rejection of Russia’s key demands.

Moscow’s massive buildup of troops and military equipment near Ukraine and its wave of simultaneous military exercises across the country have raised fears of a new Russian invasion of Ukraine. U.S. officials have warned that a Russian attack could come at “any time” and have ordered diplomatic families to leave the capital, Kyiv.

The handover of the U.S. and NATO proposals marked a crucial inflection point in the crisis, that will decide whether Putin blinks and accepts the limited wins offered to Moscow by the alliance - rather than the grand bargain he demands - or whether he will double down with the “military-technical” solution he has threatened to deal with what he calls Western aggression.

Russian Foreign Minister Sergei Lavrov said the U.S. and NATO proposals contained “some positive elements,” but only on issues of secondary concern to Moscow.

Peskov said proposals to negotiate on intermediate and shorter-range missiles “would hardly be viable” except as part of Russia’s demands for sweeping changes to NATO’s posture in Europe.

Despite the differences, “there is always need for dialogue,” he added.

Last month, Russia put demands to NATO that went well beyond its call to bar Ukraine from joining the alliance. They included ending NATO’s eastward expansion and removal of NATO forces and equipment from former Soviet and Warsaw Pact countries, in moves that would comprehensively redraw the European security architecture in Russia’s favor. Washington and NATO swiftly ruled them out.

Analysts have warned that Russia’s demands could form a pretext for military action, should diplomatic efforts founder.

But Russian foreign ministry spokesman Andrei Zaitsev said Russia had repeatedly ruled out an attack.

“We consider even the thought of a war between our people to be unacceptable,” he said.

Earlier Thursday, Dmitry Medvedev, a former president who now serves as deputy chairman of the Russian Security Council, warned that international tensions would be “seriously complicated” if the United States and NATO did not meet the Kremlin’s demand to bar Ukraine from joining the alliance.

Medvedev said no one is looking for war but that “we have practically exhausted the limits of retreat.” Referring to NATO’s expansion into Eastern Europe from 1997, he added: “They are now encroaching on our state borders.”

Peskov said Russia would not delay its response to the proposals but that it would be foolish to expect it the next day.

The Kremlin denies plans to attack and has accused NATO of aggression, but military analysts describe the massive movement of Russian military equipment from across the country to Ukraine’s doorstep as unprecedented and worrying.

The U.S. and NATO proposals offer a final hope to de-escalate the crisis after recent diplomatic meetings in Europe failed to reach a breakthrough. The written response, coordinated with Ukraine, set “out a serious diplomatic path forward, should Russia choose it,” Secretary of State Antony Blinken told reporters Wednesday.

Medvedev warned that Russia also wants guarantees that the United States or other countries would never send offensive weapons to Ukraine. “Ukraine, unfortunately, has now turned . . . into a toy in the hands of NATO and, above all, in the hands of the United States . . . [and is] used as an instrument of geopolitical pressure on Russia,” he said, adding that President Vladimir Putin would decide on Russian action.

Even as diplomacy continues, the United States and some European allies are ramping up preparations for a renewed Russian invasion of Ukraine. British Defense Secretary Ben Wallace told the BBC that he is not optimistic about the chances of achieving a diplomatic breakthrough and averting a Russian invasion, although he said there is still “a chance.”

U.S. and NATO officials have expressed alarm over a buildup of Russian troops in Belarus, north of Ukraine, ahead of major military exercises next month. The chief of the Belarusian armed forces’ General Staff, Viktor Gulevich, said Thursday that Russian forces would leave the Moscow-aligned country once the exercise is over.

Amid the tension, Ukraine’s Interior Ministry said early Thursday that five people were killed and another five were injured in a shooting by a National Guard service member in the city of Dnipro. The gunman was detained after he fled the scene carrying a weapon. Officials said in a statement that the motive for the shooting is not yet known.

U.S. officials are working with countries and companies around the world to shore up alternative energy supplies to Europe, which relies on Russian natural gas exports, in the event that Moscow responds to potential sanctions by cutting off supplies. The White House has acknowledged that there are limits to any contingency measures, as the industry grapples with logistical issues and capacity constraints.

“No question there are logistical challenges, especially moving natural gas. That’s part of our discussion with a lot of these companies and countries,” White House press secretary Jen Psaki told reporters Wednesday. “But again, these conversations are ongoing, and we don’t intend to fail on them.”

The debate over how to restrain Russian aggression has been complicated by the fact that some European countries, particularly those with closer ties to Moscow, such as Germany, have been reluctant to confront the Kremlin too directly. As Washington tries to shield its allies from possible Russian retaliation, Wallace, the British defense secretary, is in Europe canvassing support for sanctions. He is also set to travel to Russia in the coming days for talks with his Russian counterpart, Sergei Shoigu.

Berlin became the subject of scorn in Kyiv after saying it would supply 5,000 military helmets to help with Ukraine’s self-defense - as the United States and other NATO members send lethal weapons, including tons of arms and antitank missiles.

“The behavior of the German government leaves me speechless,” Kyiv Mayor Vitali Klitschko told the German tabloid Bild. “What kind of support will Germany send next, pillows?”

However, a majority of Germans support the government’s stance, according to a YouGov survey carried out on behalf of the German news agency DPA. Fifty-nine percent of respondents said Germany should not send defensive weapons to Ukraine, while 20% said they should and the remainder did not know. The poll questioned 2042 Germans between Jan. 21 and 25.

Ukraine officials have criticized Germany for blocking Estonia from dispatching German-made howitzers to Ukraine, a shipment that requires Germany’s permission.

Though officials have not detailed potential punitive measures against Moscow, a controversial target would be the Nord Stream 2 pipeline, which will carry natural gas from Russia to Germany when it is activated. Many European allies oppose the pipeline, which deepens Berlin’s reliance on Moscow.

Beijing has signaled support for Moscow, with Chinese Foreign Minister Wang Yi telling Blinken in a phone call that all sides should avoid “hyping or exaggerating the circumstances of the crisis.” The security of one country “cannot come at the cost of harming another country’s security, and regional security cannot be ensured by strengthening, or even expanding, a military bloc,” he said, according to a readout, in comments that echoed Russia’s claims about Ukraine’s aim to join NATO.

The tense situation in Ukraine also is exacerbating internal divisions in the United States, where Republican leaders are attacking President Biden for what they describe as a weak response to Russian aggression. Others in the party’s right wing, including Rep. Marjorie Taylor Greene, R-Ga., and Ohio Senate candidate J.D. Vance, are questioning why the country is getting involved in Ukraine at all.

In Ukraine, many residents are preparing for a return to the violence and unrest of 2014, when Russia annexed Crimea. If a diplomatic solution fails, they are hoping for solidarity from other European nations.

“If terrible things may happen, I just want the whole world to support us, and to be aware, to accept us if we ask them,” said Alena Krichko, who lives with her two children in Kharkiv, the country’s second-largest city, which sits less than 30 miles from the Russian border.

Pannett reported from Sydney. The Washington Post’s Chico Harlan and Stefano Pitrelli in Rome, Christian Shepherd in Taipei and Whitney Shefte in Kharkiv, Ukraine, and Loveday Morris in Berlin contributed to this report.-