WASHINGTON (AFP) - The United States State Department said Thursday that Nicaragua had expelled three American government officials earlier this week, condemning what it called an "unwarranted" move that could damage bilateral ties.

"The expulsion of three US government officials from Nicaragua on the 14th of June did occur," said State Department spokesman John Kirby. "We believe it was unwarranted and inconsistent with the positive and constructive agenda that we seek with the government of Nicaragua."

Washington has lodged a formal protest with Nicaragua's ambassador in the United States, Mr Francisco Campbell.

Mr Kirby said the three officials were on "temporary duty status" in Nicaragua and had just arrived in the Central American country.

"Such treatment has the potential to negatively impact US and Nicaraguan bilateral relations, particularly trade," Mr Kirby said.

One of the officials was identified as Professor Evan Ellis, a professor on Latin America studies at the US Army War College Strategic Studies Institute, according to the Nicaraguan newspaper El Confidencial. A source confirmed that to AFP.

Prof Ellis was said to have been in Nicaragua on official assignment to research an interoceanic canal a Chinese company based in Hong Kong has said it plans to build, to rival the one in Panama.

El Confidencial quoted Prof Ellis saying that uniformed Nicaraguan officials had taken him from his hotel to the airport for a flight out of the country, less than 24 hours after his arrival.

Nicaragua later confirmed that two US officials had been expelled. It was not clear why it did not mention three officials.

"Our government has been forced to remove two people who, being United States government officials with official passports, carried out in Nicaragua without the knowledge of or coordination with our authorities tasks that are the purview of the Nicaraguan government," the press service of President Daniel Ortega said.

Mr Ortega's left-wing government criticises the United States and is allied with Venezuela.

But America is Nicaragua's top trading partner, and the two countries cooperate in the areas of health, fighting natural disasters and combating drug smuggling.

Mr Ortega, 70, is a former rebel whose Sandinista movement in 1979 toppled US-backed dictator Anastasio Somoza.

He has been in office since 2006 and before that also had a 1985-1990 stint as president.