International leaders agreed to deliver about $1 billion in fresh financial aid for Ukraine on Tuesday to rapidly repair energy grids, water systems, roads and health centers decimated by relentless Russian strikes, the latest attempt to buoy Ukraine through what is already a brutal and dark winter.

The pledge of aid came at a one-day summit in Paris convened by President Emmanuel Macron that brought in countries outside of the usual list of Ukrainian allies. Leaders from about 50 countries attended, including Cambodia, Saudi Arabia, Bahrain, Turkey, Kuwait and Oman.

“It’s tangible proof Ukraine is not alone,” Mr. Macron said at the opening of the summit. He was flanked by Denys Shmyhal, Ukraine’s prime minister, and Olena Zelenska, Ukraine’s first lady. Leaders and diplomats from about 50 countries also attended.

“The fight you are waging is a fight for your freedom, your sovereignty,” Mr. Macron said. “But it is also a fight for the international order and for the stability of all of us.”

The Paris conference was the latest in a series of international meetings focused on the current and future reconstruction of Ukraine. On Monday, leaders from the Group of 7 wealthy democracies met virtually to agree a new system of funneling funds to Kyiv, and the European Union’s foreign ministers met in Brussels, pledging another €2 billion for military support. Weeks before, the United States pledged $53 million to rebuild Ukraine’s electricity grid at a NATO meeting in Bucharest.

What makes Tuesday’s conference and announcements different, organizers said, was the timeline. The money raised will be delivered between now and the end of March to meet Ukraine’s short-term needs. One criticism of previous aid pledges has been the length of time for delivery.

The French leader also announced the creation of the “Paris mechanism” — a platform designed to ensure that donors coordinate urgent deliveries and match them to Ukrainian needs. Hubs in Poland and several other countries will collect international donations, including generators and heat pumps, that can be swiftly shuttled into Ukraine.

President Volodymyr Zelensky, speaking from Ukraine at the conference’s opening via video feed, said that reversing the extensive damage to his country’s energy infrastructure would cost about €800 million ($840 million) and predicted that Russia was likely to “intensify its attacks” during the winter.

Ukraine’s government has estimated that it would cost $750 billion to rebuild the war-battered country, although the World Bank has put that estimate at closer to $349 billion.

Officials gathered at the Paris meeting pledged to support Ukraine for the long haul, and many reiterated the argument that Russia’s attacks on civilian infrastructure amounted to war crimes.

​​“I’m not the biggest at the table,” said Prime Minister Xavier Bettel of Luxembourg, committing €4 million in immediate aid. “But you can count on us. We are with you.”

The Swiss Parliament approved the immediate transfer of 100 million Swiss Francs ($107 million), said President Ignazio Cassis of Switzerland. Mr. Macron committed €76.5 million in immediate assistance from France, in addition to €48.5 million already pledged.