The United States has repatriated 108 Cuban migrants who were picked up at sea in recent days trying to reach American shores in unseaworthy vessels, the US Coast Guard said Monday.

The migrants were in seven rustic craft intercepted in the Florida Strait, a treacherous, shark-infested body of water that lies between Cuba and the United States, the Coast Guard said.

They were returned to Bahia de Cabanas, Cuba on Sunday in two Coast Guard patrol boats, it said.

Since the United States and Cuba announced a historic rapprochement in December 2014, there has been a surge in attempts by Cubans to reach the United States.

US law allows Cubans who reach dry land to stay and ultimately gain permanent resident status, a Cold War era policy that some would-be immigrants fear will end as US-Cuban relations normalize.

"US immigration policies have not changed and we urge people not to take to the ocean in unseaworthy vessels. It is illegal and extremely dangerous," Coast Guard Captain Mark Fedor said.

President Barack Obama's administration has repeatedly said it has no plans to change the laws governing Cuban immigration to the United States.

Since October 1, 915 Cubans have tried to enter the United States by sea, according to US statistics.

In the previous fiscal year ending September 30, 4,462 Cubans arrived by sea or tried to do so, compared to 3,940 the previous year.