The question of how to honor one of the world's longest-standing and most contentious leaders is turning into a hot potato in several countries, both former foes and allies of communist Cuba.

The omission of Obama, who helped ease tensions between Cuba and the US, is not surprising as he cannot afford to officially endorse Castro's legacy by attending the late leader's last rites. But unexpectedly, Russian President Vladimir Putin, a long-time supporter of Cuba and Castro, has also bowed out.

On Monday, Kremlin spokesman Dmitry Peskov told reporters that Putin has no plans to visit Havana, citing the Russian president's busy schedule. Instead, Vyacheslav Volodin, a close Putin ally and the speaker of the Russian State Duma or lower house of parliament, would head the Russian delegation, Peskov said.

A series of Castro memorials began on Monday as Cubans started converging on Havana's Revolution Square. Castro's ashes will go on a four-day island-wide procession before being buried in the southeastern city of Santiago on December 4, the government said.

Hailed by the socialist groups across the world as a "hero" and one of the 20th century biggest political icons, Castro was criticized by his opponents as dictator whose regime cracked down on dissidents and violated human rights in his country.

Canadian Prime Minister Justin Trudeau is one of the few Western leaders who showered praise on Castro, calling him "a legendary revolutionary and orator" and "a remarkable leader."

But Trudeau's comments caused uproar in Canada, forcing him to ditch the funeral and go on record calling the Cuban revolutionary leader a "dictator." Andree-Lyne Halle, a spokeswoman for the prime minister, said Monday that Trudeau's schedule does not permit him to attend Castro's funeral.

While the leaders of Germany, France and Britain are unlikely to travel to Havana, it is yet to be seen whether Chinese President Xi Jinping will pay his respect to the Comrade Castro who he said "will live forever."

That leaves North Korean leader Kim Jong Un. Despite calling a three-day national holiday in Castro's honor, the isolated communist nation hasn't yet hinted of any travel plans for Kim.