(Reuters) - Chad's air force chief ordered the United States to halt activities at an air base near the capital N'Djamena, according to a letter sent to the transitional government and seen by Reuters.
Chad has so far not followed the steps of juntas in Burkina Faso, Mali and Niger in ending military collaborations with France and other traditional Western allies while they strengthen ties with Russia instead.
In the letter dated April 4 to Chad's minister of armed forces, Air Force Chief of Staff Idriss Amine Ahmed said he had told the U.S. defence attache to halt U.S. activities at the Adji Kossei Air Base after "Americans" had failed to provide documents justifying their presence there.
Agreements on support for logistics and personnel did not suffice, Ahmed wrote in the letter.
"We ask you... to inform the Americans that we have made this decision," he said.
A Chad government spokesperson and the Pentagon did not immediately respond to requests for comment on the letter.
A U.S. state department spokesperson said: "We are in ongoing conversations with Chadian officials about the future of our security partnership."
"As Chad is focused on preparing for its presidential elections on May 6, we anticipate consultations on the parameters of our security cooperation after the election," the spokesperson said.
The United States has less than 100 rotational troops in Chad, focused on planning tasks for the region, a U.S. official said.
Interim President Mahamat Idriss Deby is running for election next month, making Chad the first of West and Central Africa's junta-ruled countries to organise a vote. Opposition groups have flagged concerns about its credibility.
Until now, the vast central African country has been a key partner for Western and regional militaries in a joint fight against a violent Islamist insurgency in neighbouring West Africa.
Former colonial power France still has 1,000 troops and war planes based in Chad.
It has become all the more central to Western security strategy in the region since neighbouring Niger kicked out French troops after its junta seized power in a coup last year, following similar moves by military-led Mali and Burkina Faso.
The U.S. official said it would not be ideal if they had to leave Chad but it would be far easier than a move out of Niger.
The future of the around 1,000 U.S. military personnel in Niger has been in doubt since the Nigerien authority's decision in mid-March to revoke an accord that had allowed them to operate on its territory out of two bases.
The official added that it was unclear if there was an actual desire for U.S. troops to leave Chad or if the current situation was more of a political play before the elections.
(Reporting by David Lewis, Idrees Ali and Daphne Psaledakis; Additional reporting by Mahamat Ramadane; Writing by Sofia Christensen and Alessandra Prentice; Editing by Bill Berkrot)
