The Fields medal is sometimes referred to as the Nobel Prize in mathematics.
Four mathematicians, including Ukrainian Maryna Viazovska, were awarded prestigious Fields medals on Tuesday the International Mathematical Union jury said.
France's Hugo Duminil-Copin, US-based June Huh and Britain's James Maynard were also awarded the medals at a ceremony in Helsinki.
The Fields medal, sometimes referred to as the Nobel Prize in mathematics, recognises "outstanding mathematical achievement" by under-40s and is awarded once every four years.
Viazovska is only the second woman to win the prize in its over 80-year history.
The ceremony was part of the International Congress of Mathematicians, which was initially scheduled to be held in Saint Petersburg but was moved online due to the war in Ukraine.
The award ceremony took place in Finland.
Viazovska was born in 1984 in Ukraine, then still part of the Soviet Union, and has been a professor at the Ecole Polytechnique Federale de Lausanne in Switzerland since 2017.
She was awarded the prize for solving a version of a centuries-old mathematical problem, where she proved the densest packing of identical spheres in eight dimensions.
The "sphere packing problem" dates back to the 16th century, when the question of how cannonballs should be stacked to achieve the densest possible solution was poised.
The first woman to win the prize was Maryam Mirzakhani in 2014, an Iranian-born mathematician who died three years later in 2017 after a battle with cancer.
Duminil-Copin, born in France in 1985, is a professor at the Institut des Hautes Etudes Scientifiques, focusing on the mathematical branch of statistical physics.
Carlos Kenig, President of the International Mathematical Union, said Duminil-Copin was honoured for solving "long-standing problems in the probabilistic theory of phase transitions", which according to the jury has opened up several new research directions.
Maynard, 35, is a professor at the University of Oxford in the United Kingdom and received the medal "for contributions to analytic number theory, which have led to major advances in the understanding in the structure of prime numbers and in Diophantine approximation", Kenig said.
"His work is highly ingenious, often leading to surprising breakthroughs on important problems that seemed to be inaccessible by current techniques," the union said in statement.
June Huh, 39, a professor at Princeton University in the United States, was given the award for "transforming" the field of geometric combinatorics, "using methods of Hodge theory, tropical geometry, and singularity theory", the jury said.
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