US Senior officials are warning citizens that they could be harmed if they travel to Cuba due to specific attacks that targeted US Embassy workers in Havana.

The Trump administration is banning U.S. flights to all Cuban cities but Havana in the latest move to roll back the Obama-era easing of relations, officials said Friday.

The State Department said JetBlue flights to Santa Clara in central Cuba and the eastern cities of Holguin, Camaguey would be banned starting in December. American Airlines flights to Camaguey, Holguin and Santa Clara, the beach resort of Varadero and the eastern city of Santiago are also being banned.

Flights to Havana, which account for the great majority of U.S. flights to Cuba, will remain legal.

The stated reason for the move is to prevent tourism to Cuba, which is barred by U.S. law. But it is not clear how many people take the banned flights for tourism purposes. Many are used by Cuban-Americans visiting relatives in cities far from Havana by road.

"We plan to operate in full compliance with the new policy concerning scheduled air service between the U.S. and Cuba," JetBlue said in a written statement. "We are beginning to work with our various government and commercial partners to understand the full impact of this change on our customers and operations in Camaguey, Holguin and Santa Clara."

Charter flights to destinations outside Havana are apparently not affected by the ban, but those flights tend to be more expensive and far less convenient. The other remaining legal option is a flight to Havana and then a road trip that could last as much as eight to more than 12 hours over rutted, unsafe roads, in the case of Cuba's eastern cities.

"We want to make sure that Cuban-Americans do have a route to their families. You need to enter. Havana is currently carved out for this," said Carrie Filipetti, deputy assistant secretary for Cuba and Venezuela in State Department's Bureau of Western Hemisphere Affairs. "We wanted to make sure that we took an action that would be consistent with that guidance of constraining resources that the regime has."

American Airlines said it was reviewing the U.S. decision. "We will continue to comply with federal law, work with the administration, and update our policies and procedures regarding travel to Cuba as necessary," a company statement said.

The Trump administration has been regularly tightening the six-decade-old embargo on Cuba in recent months with the stated purpose of cutting off income to the Cuban government and forcing it to cut ties to Venezuela and grant more human rights to Cuban citizens. Washington has barred U.S cruise ships visiting Cuba, sanctioned oil tankers moving petroleum from Venezuela to Cuba and permitted lawsuits against foreign companies profiting from their use of properties confiscated from Americans or from Cubans who later obtained American citizenship.

The measures have contributed to the Cuban government's chronic shortages of hard currency and were blamed for several weeks of fuel shortages on the island, but so far there is no indication that the Trump policy is having its desired effect. Cuba's security services continue to detain and harass dissenters and human rights groups say freedom of expression, assembly and other rights remain highly curtailed.

The Cuban and Venezuelan government remain tightly aligned and both have declared their intent to become even closer allies in the face of the Trump measures.

"Eager to punish Cuba's unbreakable defiance, imperialism is going after regular flights to various Cuban cities. It doesn't matter that they're affecting family relations, or the modest pocketbooks of most Cubans in both countries, or the unfair inconveniences," said Carlos F. de Cossio, head of Cuba's department of U.S. affairs. "Our response isn't changing."