A flurry of diplomacy surrounding Ukraine unfolds this week.

Ukraine has launched a new flurry of diplomacy to rally support for its war effort, with President Volodymyr Zelensky urging allies to provide more military aid and the first lady, Olena Zelenska, challenging leaders gathered at the World Economic Forum in Davos, Switzerland, to use their influence to help the country.

Their push comes as the war approaches its 12th month and Kyiv warns that Moscow could be laying plans for a new ground offensive. Ukraine is already fighting intense battles in the east of the country and confronting a withering barrage of Russian attacks on its energy infrastructure.

Mr. Zelensky, in his nightly address on Monday, said that a package of new military aid from Britain, including Challenger 2 tanks and a package of other sophisticated military equipment, “was exactly what we need.” He cited the attack on civilians in an apartment building on Saturday in the Ukrainian city of Dnipro, which killed at least 44 people, as a sign that Russia is seeking to change the direction of the war.

The “fact that Russia is preparing a new attempt to seize the initiative in the war, the fact that the nature of hostilities at the front requires new decisions in the defense supply — all this only emphasizes how important it is to coordinate our efforts,” Mr. Zelensky said.

A series of diplomatic meetings this week will offer Ukraine and its allies the opportunity to more closely coordinate support for Kyiv’s war effort. Britain’s foreign secretary, James Cleverly, is visiting Washington on Tuesday and will meet with the U.S. secretary of state, Antony J. Blinken. A gathering of Ukraine’s allies known as the Ukraine Defense Contact Group was scheduled to be held at Ramstein Air Base in Germany at the end of the week.

Ukraine and its allies are growing more worried that there is a short window to prepare for a possible Russian offensive in the spring. Russia has suffered a series of losses since September, when Ukraine recaptured significant parts of its territory in the north and east. Russia responded by targeting civilians and infrastructure as fighting on the eastern front ground to a stalemate.

On Sunday, Jens Stoltenberg, the secretary general ofNATO, said that the war was in a “decisive phase” as he vowed continued support for Ukraine. That assessment matches the view of analysts at the Institute for the Study of War, a research group that closely follows the conflict, which said in its latest daily report on Monday that “the Kremlin likely intends to take decisive strategic action in 2023.”

Britain’s decision to send tanks — which allies had declined to do for months, fearing it would provoke Moscow — has added to pressure on Germany to deliver Leopard 2 battle tanks to Ukraine. That decision lies with Germany’s chancellor, Olaf Scholz, who has said that he would do so only in coordination with Germany’s key allies.

In Davos on Tuesday, Ms. Zelenska called on world leaders, chief executives, scientists and others at the forum, which began Monday, to look around the hall and see that it was full of “people who have influence, for societies and for the world as a whole.”

“Not all of you are using this influence,” she said, “or sometimes you are using it in a way that divides even more.”

In her speech, she outlined a 10-point peace plan that had previously been announced by Mr. Zelensky in November. The plan includes the complete withdrawal of Russian forces. He is scheduled to address the forum by video link on Wednesday.

On the sidelines of the summit, Vitali Klitschko, the mayor of Kyiv, told the news agency Reuters on Monday that Kyiv’s battered infrastructure, which has been hit consistently by Russian airstrikes, was strained and could collapse “at any second.”

Mr. Klitschko’s brother Wladimir, a fellow former heavyweight boxing champion who is also attending the summit, added that Ukraine’s allies should speed up deliveries of air defense systems.

“It is important not to hesitate to give us weapons that we so need, but to deliver them the sooner the better — otherwise we will continue to lose our infrastructure and, most importantly, our best men,” he said, according to Reuters.