In Friday's disturbances, the worst outbreak of civil disorder since the revolution in 1959, groups throwing stones clashed for several hours along the Malecon, Havana's waterfront, with police and civilian vigilante brigades. Windows were smashed and shops were looted as hundreds of people marched down a main street chanting 'Freedom] Freedom]' A number of people were arrested. Later in the afternoon Mr Castro inspected the area.
At the weekend, security measures in the city were tightened, roads leading to the port were blocked and tension is reported to have increased.
The party faithful, stoical beneath a seasonal downpour, were addressed on Sunday by the Deputy Defence Minister, Ulises Rosales del Toro, who reiterated the angry allegation made by Mr Castro on Friday that the United States was behind the unrest.
Mr Castro, in a televised address on Friday, said one reason for the illegal emigration was the US embargo 'which attempted to strangle the Cuban people by starvation and lack of medicines'. He threatened to unleash a flood of Cuban refugees to the US, as he had in the 1980 Meriel boatlift which unloaded 130,000 Cubans on to the Florida shores, many of them common criminals.
Ostensibly, Sunday's rally was to honour a young policeman, Gabriel Lamoth Caballero, who was killed by hijackers who commandeered a ferry boat in Havana last Thursday to try to reach the United States. But it was also the Communist regime's fightback against the disturbances, an unwelcome indication of the potential instability of Mr Castro's 35- year-old one-party state. Divers are still searching Havana bay for the body of a second policeman killed in the hijacking.
Mr Rosales, addressing multitudes who had been mobilised block by neighbourhood block and bussed in from the surrounding countryside, repeated Mr Castro's threat to flood the US with Cuban emigrants if Washington did not halt what Havana regards as its 'malevolent' policy of encouraging illegal emigration from Cuba. Washington, he said, was only trying to cause disorder and provoke a 'bloodbath' in Cuba.
Mr Castro himself was absent from the event - on a visit to Colombia for the swearing-in of the new Colombian President. But a phalanx of senior figures in the Cuban nomenklatura, including the First Deputy President, Raul Castro, the President's brother, flanked Mr Rosales, along with a group of relatives of the dead policeman.
But Mr Rosales, chairman of Cuba's joint military chiefs and a member of the ruling Communist Party's top policy-making committee, made clear that the Cubans were keen to resolve the problem by negotiation. 'If the United States is ready to discuss serious solutions and hold honest negotiations with Cuba, we do not oppose a joint search for solutions,' he said.
Thursday's hijacking, which ended with authorities bringing the hijackers and passengers back to Havana after the vessel ran out of fuel, was the third such incident in nine days.
In Washington, US officials played down the incident, saying that Havana appeared to have calmed down and that 'Castro has backed off of his threat'. The White House chief of staff, Leon Panetta, said: 'We have made it very clear to Castro that he cannot dictate our immigration policy and we will not accept the threats he has made.'