LONDON-One of the world's foremost mathematicians, Prof Sir Michael Atiyah, has died at the age of 89.

Sir Michael, who worked at Cambridge University before he retired, made outstanding contributions to geometry and topology.

Sir Michael was a recipient of the highest honour in mathematics, a Fields Medal. He died on Friday.

His brother Joe told BBC News he had been one of the most important mathematicians of the 20th Century.

"He has been described to me by more than one professor of mathematics as the best mathematician in this country since Sir Isaac Newton," Mr Atiyah said.

Sir Michael was also a former president of the Royal Society, which is one of the highest honours a UK scientist can receive.

Prof Venki Ramakrishnan, the Royal Society's current president, described him as a "great mathematician".

"Sir Michael Atiyah was also a wonderful person who, as president of the Royal Society, showed that he was a true internationalist and a fervent supporter for investing in talent," he added.

Sir Michael was best known for his co-development of a branch of mathematics called topological K-theory and the Atiyah-Singer index theorem.

His research also involved deep insights relating to mathematical concepts known as "vector bundles".

'Greatly missed'

His work in these areas has helped theoretical physicists to advance their understanding of quantum field theory and general relativity.

He was also an occasional poet - a talent which was highlighted by Prof Robbert Dijkgraaf, the director of the Institute of Advanced Studies in New Jersey, where Sir Michael once worked on the research centre's website.

"Sir Michael Atiyah was a dear mentor, friend, and role model, unmatched in intellect and energy," he said.

"His legacy in mathematics and physics will last forever. His passing is a terrible loss, and we extend our deepest condolences to his family.

"He will be greatly missed by friends and colleagues around the world."