SANTIAGO DE CUBA, July 26 (Xinhua) -- The United States is tightening its grip on Cuba and other leftist Latin American countries, Cuba's ex-president Raul Castro warned here on Thursday.

Speaking at a ceremony marking the National Rebellion Day, Castro, who continues to serve as the first secretary of the Central Committee of the Communist Party of Cuba, said Washington's attempt to isolate the country calls for a strong response.

"For us, as well as Venezuela and Nicaragua, it is clear the grip is tightening and our country must be clear about responding with force," Castro told a crowd of more than 10,000 gathered outside the historic Moncada Barracks in the eastern city of Santiago de Cuba.

Cuban President Miguel Diaz-Canel was also present, honoring the day that kicked off the Cuban Revolution.

"Since July 26, 1953, we Cubans have been forged in a constant battle. History has demonstrated that we could, we can and we will prevail," said Castro.

Havana and Washington officially resumed diplomatic ties in 2015 under the Obama administration. However, their relationship has deteriorated since U.S. President Donald Trump took office.

Tensions between the two countries have grown since August 2017, when the United States accused Cuba of carrying out "acoustic attacks" against its diplomatic personnel, "which nobody has been able to substantiate," said Castro.

The U.S.-led trade embargo against Cuba has been stepped up, with countries or companies that have financial transactions with the island nation sanctioned especially, Castro said.

He also condemned U.S. efforts to undermine Latin American regional organizations.

The way to counter U.S. efforts to dominate the region is "to never neglect the unity of the revolutionaries," Castro said, expressing solidarity with Venezuela and Nicaragua, as well as Brazil's ex-president Luiz Inacio Lula da Silva.