"I think that a new and disgusting form of fascism is emerging with considerable force at this moment in human history," Castro wrote in a column in the newspaper Granma titled "Palestinian Holocaust in Gaza."
Castro's article appeared as a 72-hour truce took hold in the Gaza Strip, with Israel withdrawing troops after a month of fighting with the militant group Hamas that killed at least 1,867 Palestinians and 67 people in Israel.
"Maybe it hopes that the complicity of the North American (US) empire will be ignored in this shameless massacre?" the 87-year-old former president said.
"There are facts that reflect the near total inability of the United States to face the current world problems," said Castro, who handed over power to his brother Raul in 2006 for health reasons.
Communist Cuba broke diplomatic relations with Israel in 1973 after the Yom Kippur War.
