Nobel Prize-winning chemist Ahmed Zewail dies at 70

Egyptian-American Ahmed Zewail, a renowned Nobel Prize recipient for chemistry and the first US science envoy to the Middle East, has died on Tuesday at 70 years old, his spokesman told an Egyptian state-owned broadcast network.

"The cause of death is unknown ... whether it is cancer or something else ... His doctor said his condition was stable the last time I called him last week," spokesman Sherif Foad said.

Zewail's work led to the birth of the research area called femtochemistry, which studies the chemical reactions that occur over an incredibly short period of time, known as a femtosecond, which is one quadrillionth, or one millionth of one billionth, of a second.

Zewail, a naturalised US citizen, won the Nobel Prize for chemistry in 1999, making him the third Egyptian to win a Nobel Prize and the country's first scientist to do so.

His work showed that it is possible with rapid laser technique to study in slow motion how atoms in a molecule move during a chemical reaction.

"Egypt has today lost one of its faithful sons and a brilliant scholar" who devoted his life to scientific research, Egyptian President Abdel Fattah al-Sisi said in the statement.

Born in the northern Egyptian town of Damanhur in 1946, Zewail studied chemistry at Alexandria University before moving to the US in 1969 where he gained his doctorate from the University of Pennsylvania in 1974.

In 2009, he was appointed to Obama's Council of Advisors on Science and Technology, and later that year he was named the US's first science envoy to the Middle East.

Up to his death Zewail worked at the California Institute of Technology. Zewail was married with four children. His body will be repatriated to Egypt.