US tightening grip on Cuba: Raul Castro

"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 10,000 strong crowd gathered outside the historic Moncada Barracks in Santiago de Cuba.

He was speaking at a ceremony marking the National Rebellion Day, Xinhua news agency reported.

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 will be faced with resistance.

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

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

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

The US-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 US efforts to undermine Latin American regional organisations.

The way to counter US 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 former President Luiz Inacio Lula da Silva.