Updated

A small ferry boat hijacked in Havana Bay and forced to sail toward Florida had returned to Cuba Thursday after Cuban authorities chased it some 30 miles into international waters.

The boat left international waters late Wednesday under Cuban government escort, a U.S. Coast Guard official in Miami said, speaking on condition of anonymity. He declined further comment.

It was unclear whether the hijackers had surrendered.

FBI agents had waited nearby on a U.S. Coast Guard cutter as Cuban authorities tried to persuade the hijackers to give up. The men had threatened to throw some of the passengers overboard if they did not get their way, the Cuban government said in a written statement on Wednesday.

As the boxy, flat-bottomed ferry struggled through choppy seas on Wednesday, the hijackers had radioed a command post of the Cuban coast guard to demand another boat and enough fuel to reach the United States, Cuba's Prensa Latina news service said.

The seizing of the vessel came a day after a Cuban passenger plane was highjacked to Key West, Fla., by a man who allegedly threatened to blow up the aircraft with two grenades that later turned out to be fake. Another Cuban plane was hijacked to Key West less than two weeks before.

The string of hijackings coincides with a new crackdown on dissent in Cuba and rising tensions with the United States. Some 78 dissidents have been arrested in recent weeks on charges of conspiring with U.S. officials, and the first round of trials begins Thursday.

In the past, Cubans have taken advantage of periods of U.S.-Cuban friction to try to flee the island.

An FBI spokeswoman in Miami said that agency negotiators flown by helicopter to the scene of the ferry standoff were standing by on the Coast Guard cutter while Cuban authorities dealt with the situation. The ferry was drifting in international waters about 60 miles off Key West, she said.

Fidel Castro's government said it would handle the crisis in the Florida Straits. The U.S. Coast Guard confirmed that Cuba had taken the lead role but said it was ready to assist.

"What we won't do in any case is to use measures of force that put in danger the lives of the people aboard this boat," the Cuban statement said. It said 50 passengers were on board.

The cooperation between agencies from both countries underscored the worries both American and Cuban officials have about the recent rash of hijackings.

In a highly unusual move, the top U.S. diplomat in Havana on Wednesday night warned Cubans not to undertake any more hijackings, telling them in a message read on communist-run television that they would be prosecuted and lose the right to seek American residency.

The message by James Cason, chief of the U.S. Interests Section, demonstrated growing worries about the possibility that such hijackings could end in violence or spark a migration crisis.

The high seas drama began early Wednesday when a group of people armed with three pistols and at least one knife hijacked the ferry, Havana said in a statement read on state television.

The ferry provides service between Havana and the small communities of Casablanca and Regla on the other side of Havana Bay.

FBI spokeswoman Judy Orihuela said Cuban officials told her agency that there were 15 to 20 people aboard the 45-foot boat. There was no immediate explanation for the differing figures.

The Cuban statement said two Cuban Coast Guard boats had followed the ferry out to the high seas, where they will remain to provide assistance in an emergency or to escort the ferry back to Cuba.

Several ferry boats were hijacked to the United States in 1994, when some 35,000 Cubans headed toward Florida in dilapidated boats and rafts. The wave of illegal migrants subsided only after the United States agreed to send back Cubans picked up at sea.

However, Cubans continue to try to reach U.S. shores by boat. On March 4, 20 were found stranded on a tiny island at the southern end of Biscayne National Park after their 25-foot boat ran out of gas. On Feb. 7, four Cuban coast guardsmen sailed their patrol boat to Key West and defected.