The United States on Thursday imposed sanctions on Cuba's defence minister for repressing peaceful protests. US President Joe Biden that the step was just the beginning of a series of punitive measures against Cuba.

The US Treasury Department said its Office of Foreign Assets Control froze the assets of minister Alvaro Lopez Miera and the Special National Brigade (SNB), a division of Cuba's interior ministry, in relation to human rights abuses committed during a crackdown on protests on the island earlier in July.

Biden issued a statement warning that the United States would continue to sanction those who were responsible for the 'oppression of Cuban people'.

Also read: US looks to expand embassy in Cuba after protests

The move was taken under provisions in the Magnitsky Act. The act allows a US President to take action if they feel that human rights are being abused.

Biden said his administration targeted Lopez Miera and the SNB -- a special forces unit nicknamed the Black Berets -- because they were 'driving the crackdown' against protesters who took to the streets by the thousands in rare public demonstrations against the communist government.

This comes after the United States said Tuesday it was looking to expand its embassy staff in Cuba and studying ways to let Cuban-Americans bypass the government in sending back money following unprecedented demonstrations.   

Havana, under US sanctions since 1962, has blamed the show of discontent on Washington pursuing a "policy of economic suffocation to provoke social unrest."  

The rallies against the communist government are the largest since the Cuban revolution of the 1950s and come as the country endures its worst economic crisis in 30 years, with chronic shortages of electricity, food and medicine, just as it records a spike in coronavirus infections.  

"Born to conquer and not to be conquered!" shouted the crowds at the rally, which had gathered at dawn on the Malecon, Havana's famed oceanfront boulevard.

Shortly before the rally began, police arrested a man who shouted "Patria y Vida" ("Homeland and Life"), the title of a protest rap song which has become the anthem of anti-government demonstrators.

The official newspaper Granma said similar rallies were called in other cities including Santiago de Cuba, Bayamo, Camaguey and Santa Clara.