Ecuador's President Rafael Correa has ordered all US military officers to leave the country by the end of month and canceled a security cooperation program with the Pentagon, US officials said on Friday.

"At the request of the government of Ecuador, our bilateral security cooperation programs in Ecuador are currently coming to a close," Pentagon spokesman Colonel Steven Warren told AFP in an email.

The defense program had to be shut down by the end of April, he said.

An American embassy official in Quito had earlier said Quito had demanded 20 US Defense Department personnel leave the country, and Ecuadoran officials had said they had until the end of the month to depart.

The move is the latest setback for US-Ecuador relations, which have been strained since Correa entered office in 2007. His government has expelled American diplomats and rebuffed a trade deal with Washington, while accusing the United States of imperialist ambitions.

The United States respects Ecuador's right as a "sovereign" nation to expel the US military staff, but regrets that the move "will severely limit our bilateral cooperation on issues related to security," Jeffrey Weinshenker, a spokesman at the US embassy in Quito, said in a statement.

He added: "The Ecuadoran government has made clear that it no longer wants this security assistance.

"The US government is reducing our security cooperation programs and moving those assets to another location," the diplomat said.

US military assistance over four decades in Ecuador had included technical training and had helped counter drug-trafficking, human trafficking and transnational crime, according to US officials.

The expulsions make good on a months-old threat by Correa to drastically pare back the presence of US military officers and staff in Ecuador, citing concerns about US "espionage" and "American imperialism."

Quito in January said it wanted to reduce the number of US military staff on its territory, and also warned it would not allow American "espionage equipment" on its soil.

Prior to the expulsion orders, there were about 50 US military staff in Ecuador, according to officials in the Ecuador government.

Correa said he became aware of what he described as a bloated US military presence in his country after learning that four Pentagon personnel were aboard an Ecuadoran military helicopter that came under fire in October near the border with Colombia.

Bilateral relations also were damaged by the controversy over US electronic surveillance of foreign governments, which was brought to light by fugitive intelligence leaker Edward Snowden.

In 2009, Correa refused to renew a lease that had allowed US forces to operate out of Manta, an important base for its counter-narcotics efforts in South America.

In 2012, the Ecuadoran president angered Washington when his government granted asylum at its embassy in London to Julian Assange, the founder of the anti-secrecy website WikiLeaks, which published a trove of classified US documents.