U.S. homeland security secretary Alejandro Mayorkas warned Cubans and Haitians against attempting to migrate to the U.S. by sea on Tuesday, amid domestic upheaval in both nations.

“The time is never right to attempt migration by sea,” Mayorkas said at a press briefing at U.S. Coast Guard Headquarters. “To those who risk their lives doing so, this risk is not worth taking.”

Even asylum-seekers who can establish a credible fear of government persecution will be resettled in a third country, Mayorkas said.

“If individuals make, establish a well-founded fear of persecution or torture, they are referred to third countries for resettlement. They will not enter the United States,” Mayorkas emphasized.

The comments come after Haiti’s president was assassinated earlier this month, and government officials requested U.S. troops to help protect infrastructure during potential unrest.

Meanwhile this week, Cuba saw the largest anti-government protests in decades. Thousands of Cubans fled to Florida by sea following protests in 1994.

While the U.S. has not yet recorded a major surge in Haitian or Cuban migrants, Mayorkas said the U.S. Coast Guard has expanded its presence in the Florida Straits and Caribbean Sea to monitor for potential migrant activity.

“Any migrant intercepted at sea, regardless of their nationality, will not be permitted to enter the United States,” Mayorkas said.

The Biden administration is already contending with a major increase in illegal immigration on the U.S.-Mexico border. U.S. Border Patrol agents encountered 180,000 migrants over the course of May, close to 179,000 in April, and over 173,000 in March.