"I extend my deepest condolences to the government and the people of Cuba on the sad demise of Fidel Castro. May his soul rest in peace," Modi said in a tweet.
"We stand in support with the Cuban government and the people in this tragic hour. Fidel Castro was one of the most iconic personalities of the 20th century. India mourns the loss of a great friend," he said.
Castro, who ruled Cuba as a one-party state for almost half-a-century before handing over power to his brother Raul in 2008, and his small army of guerrillas overthrew the military leader Fulgencio Batista in 1959 to widespread popular support and declare the revolution to be Marxist-Leninist in nature.