Last week, Castro demanded that the United States unconditionally return the Guantanamo Bay military base to Cuba in an article published on the CubaDebate website.
Castro also criticized the United States for its policies in the Middle East, accusing Obama of supporting Israel in its "genocide" of the Palestinian people in the Gaza Strip.
In his new article, Contradictions between Obama's Policies and Ethics, the ailing revolutionary questioned U.S. policy toward Cuba and how long the economic blockade, imposed 46 years ago, would last.
Obama has said relations between Washington and Havana need to be normalized before the U.S. trade embargo could be removed.
Another of Fidel's concerns centered on U.S. energy policy, mainly regarding biofuels, and he questioned whether U.S. plans to invest heavily in alternative energy sources would satisfy America's day-to-day demands. He also speculated that a move to renewables could create problems for countries that depend on exporting oil to the United States for their income.
Castro emphasized that thanks to "media terror" any criticism on his part "is considered an angry attack and accusation," even if his words are expressed "honestly and with respect." He added that even though he is "an old politician and fighter," he has "not committed any sins by expressing his thoughts."
Castro said after Obama's inauguration that he was "an honest man with good intentions" and said he hoped the new U.S. president would not repeat the mistakes of his predecessors.
Obama issued instructions to close the controversial Guantanamo prison, used to hold terrorist suspects, in one of his first acts after taking office. However, the closure will not include the Guantanamo Bay Naval Base, where some 10,000 U.S. military personnel are stationed.
Fidel Castro is famous for his criticism of the United States, and Obama is the 10th president to come under fire since the Cuban Revolution in the 1950s. The present Cuban leader, Fidel's younger brother Raul, officially became Cuba's president in February 2008 after Fidel ceded power to him in July 2006 following surgery.