The U.S. Coast Guard continues to search the Florida Straits for some 30 Cuban rafters who disappeared more than four days ago. Hopes of finding the would-be illegal migrants has faded.

Tuesday, the Coast Guard spotted an overturned speedboat 70 kilometers southeast of Key West, Florida. The boat matches a description of a vessel believed to have been used by smugglers to transport the missing rafters from the western Cuban province of Pinar del Rio.

The perilous journey began either late Friday or early Saturday, a time when rough seas were reported in the Florida Straits.

Life jackets and other articles have been found near the capsized speedboat but there is no sign of the illegal immigrants. Some relatives in south Florida said they knew beforehand of the planned voyage, and that it included at least a dozen children.

Many of the relatives said they have lost hope that their missing loved ones will be found. Coast Guard spokeswoman Anastasia Burns said the fact that no survivors have been spotted is discouraging, but added that no decision has been made to abandon the search and rescue effort. "I can't speculate on how long the search effort will continue. I know that our crews are still out there searching, and we are going to try our best to find these people," she said.

Federal authorities have attempted to crack down on illegal immigrant smuggling from Cuba, which has surged in recent years. The U.S. Attorney's office in Miami said, if apprehended, those who organized the ill-fated journey will be prosecuted to the full extent of the law.