Ukrainian President Volodymyr Zelenskyy said his country has lost 31,000 soldiers since Russia’s full-scale invasion started two years ago as he stressed that a decision from the U.S. Congress on $60 billion in aid was needed within a month.

Zelenskyy said Ukraine has a "clear plan” for 2024, while making a blockbuster claim that parts of its 2023 battle strategy had been leaked to Russia.

With the war now in its third year, Russia has gained fresh momentum, exploiting Kyiv’s deficit of ammunition and shortage of troops. U.S. support, a crucial lifeline, faces formidable obstacles in the Republican-led House of Representatives, even after a joint $95 billion package for Ukraine, Israel and Taiwan cleared the Senate.

"When we talk about U.S. assistance, we should understand that it’s not financial support, mainly it’s weapons,” Zelenskyy told reporters in Kyiv on Sunday during an extended news conference.

"The Patriot air-defense system costs $1.5 billion, but you can’t buy it without the U.S. and there are no similar systems in the world. We can find money, but we won’t find such an amount of weapons.”

As military supplies to Ukraine are dwindling, Russian forces scored a symbolic victory this month when Ukraine pulled soldiers out of the embattled eastern city of Avdiivka after months of combat. Kremlin troops are probing Ukrainian defenses elsewhere along the 1,200-kilometer (746-mile) front-line.

The Ukrainian president said that 2024 will determine how the war will end, and called U.S. elections in November a potential tipping point.

"It will be difficult for us in the coming months because there are fluctuations in the U.S. that have an impact on some countries, though the European Union showed it is capable of being a leader with its support,” Zelenskyy said.

Ukraine expects Russia to "prepare counteroffensive actions at the end of May or the beginning of summer,” Zelenskyy said, vowing that his forces would be ready to fight. "The tipping point will be elections in the U.S., and then we will understand what will happen afterward,” he added.

Zelenskyy said Ukraine needs two or three types of weapons to stop Russia’s offensive and break its defensive lines.

"If Ukraine gets 10 Patriot systems for key industrial centers, if we can use them closer to the battlefield, they won’t be able to advance, we would crush their defensive lines,” he said. "It would radically change the situation.”

The Ukrainian leader said that his government doesn’t have precise data on how may civilians have lost their lives in the past two years because some areas are occupied, though the figure is "tens of thousands killed and murdered.”

While Zelenskyy disclosed the first official figure for military losses in many months, he declined to also pinpoint the number of wounded, saying that would help the Russian military.

The Ukrainian president claimed that some plans for Kyiv’s 2023 counteroffensive in the country’s southeast had been leaked to Russia.

"I will be open with you: our counteroffensive actions in the fall of last year were on the Kremlin’s table before those counteroffensive actions started,” Zelenskyy said, without saying who he thought was behind the leak.