Ecumenical Patriarch Bartholomew I expressed the view during his sermon at the new Orthodox Church in Havana on Sunday.
The Orthodox leader said: "The blockading of peoples and countries by society in general from other nations on earth is a historical mistake."
"And the problems between nations and countries, like those between people, are resolved through dialogue."
In the four-hour ceremony filled with centuries-old pageantry, the head of Greek Orthodoxy also consecrated the tiny limestone Cathedral of Saint Nicholas.
The United States has enforced an economic embargo against Cuba since 1961.
Earlier on Sunday, Cuban President Fidel Castro gave Bartholomew I a key to the church built by his communist government.
Former Greek King Constantine and his family attended the consecration, along with wealthy Greek American businessmen and hundreds of Orthodox Christians who travelled to Cuba for the event from the United States and Greece.
There are only a handful of Orthodox Christians living in Cuba, and most are Russians. Fewer that 50 Greek Orthodox followers call the island their home.
Bartholomew praised Castro for recognizing the Orthodox Church in Cuba for the first time since his 1959 revolution turned the island into a communist-run atheist society.
Today's consecration may affect
relations with the Catholic Church
Cuba relaxed restrictions on religious practices a decade ago, after the collapse of the Soviet Union plunged the island into a severe economic crisis, and officials pointed to the new church as proof of their commitment to religious freedom.
A Western diplomat in Havana said Castro's gift to Greek Orthodoxy was a poke in the eye to the Roman Catholic Church, the predominant religious institution in Cuba.
The Vatican has been at odds with the government, which has repeatedly denied its requests to build new churches and have access to the state-run media and schools.
The church, built with Byzantine arches and decorated with Greek mosaics, icons, candelabra and a hand-carved wooden altar, is the first built from scratch under Castro's rule.
The 77-year-old Cuban leader, dressed in a grey business suit, received as a gift from the patriarch a blessed cross of Saint Andrew, founder of the Orthodox Church.
The orthodox patriarch's visit is the most important to Cuba by a religious leader since Pope John Paul's historic trip six years ago to the day in 1998.
In a gesture to the Pope, Cuban authorities later released 200 political prisoners.
Cuban dissidents seeking democratic reform of Cuba's one-party system called on the patriarch to press Castro to release 75 opponents jailed last year in a political crackdown.
Bartholomew has not requested the release of prisoners, a spokesman said, but he mentioned the right to dissent in his speech at the doors of the church.
"The Gospel's message is one of respect for the human being and his rights, his freedom, his dignity and his right not to agree," he said.