Cuban diplomat says Havana is ready for dialogue with Washington, but certain things are off the table, including the constitution and its socialist government.

Cuba and the United States are in communication, but the exchanges have not yet evolved into a formal “dialogue”, a Cuban diplomat has said, as US President Donald Trump stepped up pressure on Havana.

Carlos Fernandez de Cossio, Cuba’s deputy foreign minister, told the Reuters news agency on Monday that the US government was aware that Cuba was “ready to have a serious, meaningful and responsible dialogue”.

De Cossio’s statement represents the first hint from Havana that it is in contact with Washington, even if in a limited fashion, as tensions flared in recent weeks amid Trump’s threats against the Cuban government in the aftermath of the US military’s abduction of Venezuelan leader Nicolas Maduro, Cuba’s longstanding ally.

“We have had exchange of messages, we have embassies, we have had communications, but we cannot say we have had a table of dialogue,” de Cossio said.

In a separate interview with The Associated Press news agency, De Cossio said, “If we can have a dialogue, maybe that can lead to negotiation.”

The deputy minister also stressed that certain issues are off the table for Cuba, including the country’s constitution, economy, and its socialist system of government.

On Sunday, Trump indicated that the US had begun talks with “the highest people in Cuba”.

“I think we’re going to make a deal with Cuba,” Trump told reporters at his Mar-a-Lago estate in Florida.

Days earlier, Trump had referred to Cuba in an executive order as “an unusual and extraordinary threat” to US national security, and warned other countries he would impose more tariffs on them if they supplied oil to Cuba.

On Monday, Trump reverted to issuing threats to Havana, announcing at the White House that Mexico “is going to cease” sending oil to Cuba, a move that could starve the country of its energy needs.

Mexico, which has yet to comment on Trump’s latest statement, is the largest supplier of oil to Cuba.

Mexico had repeatedly said that it would not stop shipping oil to Cuba for humanitarian reasons, but also expressed concern that it could face reprisals from Trump over its policy.

In recent weeks, the US has moved to block all oil from reaching Cuba, including from Cuba’s ally Venezuela, pushing up prices for food and transportation and prompting severe fuel shortages and hours of blackouts, even in the capital, Havana.

Responding to Trump’s threat regarding oil supplies, Cuba’s De Cossio said that the move would eventually backfire.

“The US… is attempting to force every country in the world not to provide fuel to Cuba. Can that be sustained in the long run?” de Cossio said to Reuters.

The US has imposed decades of crushing sanctions on Cuba, but a crippling economic crisis on the island and stepped-up pressure from the Trump administration have recently brought the conflict to a head.