The White House said Biden told Zelenskyy he was exploring additional macroeconomic support to help Ukraines economy as it comes under pressure as a result of Russias military buildup.

Meanwhile, the United States announced that the U.N. Security Council will hold an open meeting Monday on what U.S. Ambassador Linda Thomas-Greenfield called Russias threatening behavior. She said the deployment of more than 100,000 troops along Ukraines border and other destabilizing acts pose a clear threat to international peace and security and the U.N. Charter.

Kremlin spokesman Dmitry Peskov told reporters earlier that the response from the U.S. and a similar one from NATO left little ground for optimism. But he added that there always are prospects for continuing a dialogue, its in the interests of both us and the Americans.

White House press secretary Jen Psaki was circumspect when asked whether the Biden administration saw a sliver of hope in that the Russians said they would keep communications open even as they said that they lacked optimism..

We dont know if the Russians are playing games on diplomacy. We hope not, Psaki said.

Foreign Minister Sergey Lavrov said the U.S. response contained some elements that could lead to the start of a serious talk on secondary issues, but emphasized that the document contains no positive response on the main issue. Those are Moscows demands that NATO not expand and that the alliance refrain from deploying weapons that might threaten Russia.

Lavrov said top officials will submit proposals to Putin. Peskov said the Russian reaction would come soon.

The evasive official comments reflect the fact that it is Putin who will single-handedly determine Russias next moves. He has warned of unspecified military-technical measures if the West refuses to heed the demands.

Peskov added that Putin and Biden will decide whether they need to have another conversation following two calls last month.

Ukraines Foreign Minister Dmytro Kuleba said Kyiv had seen the U.S. response before it was delivered to Russia and had no objections. He tweeted it was important that the U.S. remains in close contact with Ukraine before and after all contacts with Russia.

On a visit to Denmark, Kuleba emphasized his countrys need to strengthen its defenses.

This crisis is a moment of truth, and this is why we speak about weapons, he said. This is why we speak about economic sanctions. This is why we speak about the consolidated position of all of us, so that President Putin sees that there are no weak links in our defensive chain.

Germanys Foreign Minister Annalena Baerbock said during a parliamentary debate on Ukraine that her government is closely coordinating its policy with allies, considering a range of options that could include the new Nord Stream 2 Russian gas pipeline to Germany.

While the diplomacy sputters on, so too do maneuvers that have escalated tensions. Russia has launched a series of military drills involving motorized infantry and artillery units in southwestern Russia, warplanes in Kaliningrad on the Baltic Sea, dozens of warships in the Black Sea and the Arctic, and Russian fighter jets and paratroopers in Belarus.

NATO said it was bolstering its deterrence in the Baltic Sea region, and the U.S. ordered 8,500 troops on higher alert for potential deployment to Europe.

As war fears mounted, thousands of Ukrainians expressed their resolve to stand up to the Russian pressure under the hashtag #UkrainiansWillResist on Twitter and Facebook .

No one will force Ukrainians to accept the Kremlin ultimatum, wrote Andrii Levus, who initiated the campaign.

Ukraines Interior Ministry has organized training on acting in emergency situations, with an emphasis on dealing with explosives.

Beyond concerns about a possible Russian offensive in Ukraine, there also has been speculation that Moscows response could include military deployments to the Western Hemisphere.

While a senior Russian diplomat recently refused to rule out such deployments to Cuba and Venezuela, a top Putin associate expressed skepticism Thursday at that prospect.

Cuba and Venezuela are aiming to come out of isolation and restore normal relations with the U.S. to a certain extent, so there cant be any talk about setting up a base there as happened during the Soviet times, Dmitry Medvedev, a deputy head of Russias Security Council, told Russian media.

While he charged that the West is using Ukraine as a way to contain Russia, he somberly acknowledged that a Russia-NATO conflict would be the most dramatic and simply catastrophic scenario, and I hope it will never happen.

While concerns about a possible Russian attack linger, a separatist conflict simmers in Ukraine. Following the 2014 ouster of a Kremlin-friendly president in Kyiv, Moscow annexed Ukraines Crimean Peninsula and backed an insurgency in the countrys eastern industrial heartland. Fighting between Ukrainian forces and Russia-backed rebels has killed over 14,000 people, and efforts to reach a settlement have stalled.

Since the conflict began, Russia has been accused of sending troops and weapons to the separatists, something it has denied. On Thursday, Peskov wouldnt comment on a proposal from the Kremlins main political party, United Russia, which suggested that Moscow respond to the delivery of Western weapons to Ukraine by sending arms to the rebels. He added that Putin is aware of the proposal but had no immediate reaction.

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Associated Press writers Aamer Madhani and Matthew Lee in Washington, Edith M. Lederer at the United Nations, Yuras Karmanau in Kyiv, Ukraine, Jan M. Olsen in Copenhagen, Denmark, and Frank Jordans in Berlin contributed.