Donald Trump warned in a tweet on Monday that he would terminate the 2014 deal that reopened Cuban-American relations if Havana is unwilling to negotiate a better agreement.

Trump's tweet

The tweet reaffirms Trump's hardliner stance on U.S.-Cuba relations, which became evident on Saturday when he released a statement in response to Fidel Castro's death that condemned him for oppressing his people.

"If Cuba is unwilling to make a better deal for the Cuban people, the Cuban/American people and the U.S. as a whole, I will terminate deal," the tweet reads.

Kellyanne Conway, Trump's former campaign manager and senior advisor, commented this weekend on Trump's stance, saying "on the issue of diplomatic relations being re-opened with Cuba, what President-elect Trump says is that he'd be open to that himself, but that we got nothing in return."

"We're allowing commercial aircraft there. We pretend that we're actually doing business with the Cuban people now when, really, we're doing business with the Cuban government and the Cuban military. They still control everything," she said.

Landmark commercial flights to Cuba from the United States resumed Monday morning after more than a half-century of interruption.

JetBlue's first commercial flight to Havana, Cuba took off from John F. Kennedy airport just before 9 a.m. Monday. American Airlines is offering its own one-hour flights from Miami to Havana on Monday.

Delta Airlines will soon follow suit when it begins offering regular flights to Cuba from the United States on Dec. 1.

The Cuban government announced that Castro's ashes will be buried Sunday at the Santa Ifigenia cemetery in Santiago de Cuba.

for the latest on the markets.