Concern is mounting in America over the fate of 15 Cuban dissidents jailed during a crackdown this weekend on opposition leaders by the island’s communist strongman, Fidel Castro. Among the detained are leaders of the historic May 20 pro-democracy gathering in Havana, and some Cuban-American leaders in Washington said yesterday that their imprisonment was evidence that tensions on the island nation are reaching a breaking point.

According to organizers at the Miami based support center for the Assembly to Promote Civil Society in Cuba – an association of 365 independent Cuban civic organizations that, on May 20, held an unprecedented meeting of the island’s pro-democracy movement – 29 dissidents were arrested Friday as they prepared to demonstrate in front of the French Embassy in Havana. The detained included the three principal organizers of the May 20 gathering: Martha Beatriz Roque Cabello, Rene Gomez Manzano, and Felix Bonne Carcasses. All three have been political prisoners during Mr. Castro’s regime.

As of yesterday evening, 14 of the 29 dissidents jailed on Friday, including Ms. Roque, had been released, Miami support coordinators said. According to reports from Mr. Gomez’s brother, Jorge Gomez Manzano, both Messrs. Gomez and Bonne remained in Cuban facilities without any indication that they would be released. Ms. Roque, 59, was reported to be at home but suffering from low blood pressure and other ailments as a result of her detention.

On Saturday, the American government denounced the crackdown as an act of “deplorable repression,” and, in a statement from a deputy spokesman for the State Department, Adam Ereli, urged the Cuban government to “immediately free all of those arrested.”

“We urge other countries to join us in condemning these acts,” the statement continued.

According to Cuban-American leaders in Congress, condemnation from other countries – particularly E.U. members – will be vital in the efforts to liberate the detainees and bring democracy to Cuba.

“Our European allies have great leverage over the Cuban regime,” Rep. Ileana Ros-Lehtinen, a Republican of Florida, said, referring to the economic investments and tourism business Europe sends to Cuba. “They’ve said they’re interested in human rights. They’ve talked the talk; let’s get them to walk the walk and push the Castro regime on this latest roundup.”

Another Cuban-American congressman, Rep. Lincoln Diaz-Balart, a Republican of Florida, said there was a particular burden on Europe to step up and take action against the detentions in light of the E.U. decision last month to grant Mr. Castro a year of “constructive dialogue” before reconsidering its ban on high-level diplomats’ visits to Cuba and whether to open embassies in Havana to Cuban dissidents.

According to an Agence France-Presse report out of Havana, the demonstration at the French embassy that resulted in Friday’s crackdown was a protest of, among other policies, the French ambassador’s decision to invite Mr. Castro’s foreign minister, Felipe Perez Roque, to the embassy’s Bastille Day celebration while excluding members of the opposition movement.

Within the European Union, the most vocal opponents of Europe’s decision to engage Mr. Castro on equal footing have been the Czechs. The Czech ambassador to America, Martin Palous, said yesterday of the roundup: “The E.U. should send a very clear signal to the Cuban government that these types of actions are absolutely unacceptable, and that all of these people should be immediately released.”

“I think it’s very clear,” Mr. Palous said, “that those who have been arguing in favor of more ‘constructive’ and ‘outreaching’ policies toward Cuba should learn their lesson.”

In light of this weekend’s crackdown, that policy, Mr. Diaz-Balart said, “has been shown to be the pathetic blank check appeasement of Castro that it is.” As a result, Mr. Diaz-Balart said, much of the diplomatic effort in Washington to bring about the release of the dissidents in coming days “will be focused on Europe.”

Because Washington had been waiting for confirmation of the arrests over the weekend, the congressman said, he expected action from the administration and other organs of government to begin in earnest today. Mr. Diaz-Balart’s brother, Rep. Mario Diaz-Balart, a Republican of Florida, said America was “looking at all options” for bringing about the dissidents’ release.

In the aftermath of Hurricane Dennis, much of Cuba lay in ruin, and Mr. Castro’s refusal of humanitarian aid from both America and the European Union left many Cubans to brave the tropical summer without water, electricity, and other vital infrastructure. Frustration from poor conditions, plus the stepped-up efforts of the Cuban democracy movement, Mr. Diaz-Balart said, meant that “it’s a crisis looming, and the regime has nowhere to go.”

“You know the phrase ‘the darkest hour is right before the dawn’?” the congressman said. “This is definitely the darkest hour.”