France has sent about 150 supplementary troops to Chad as a «precautionary measure» in response to a rebel offensive in the central African nation, a French Defense Ministry official said Friday. The troops, stationed in Gabon, arrived in the Chadian capital, N'Djamena, early Friday morning aboard two transport planes and are to help «respond to the evolution of the situation» on the ground in Chad, Defense Ministry spokesman Col. Thierry Burkhard said. The troops were not to take any combat role and were in Chad to «if it should prove necessary, assure the security of our citizens» there, Burkhard was quoted as saying by the Associated Press. Another French unit stationed in the Gabon capital, Libreville, was on alert and could be moved to Chad if the situation there further deteriorates, he added. The move comes a day after France raised the alert level for its military forces in Chad after intelligence reports noted rebels moving toward the African country's capital. Also Thursday, the U.N. refugee agency evacuated staff in eastern Chad _ who were working with refugees from neighboring Darfur _ after attacks by Chadian rebel groups. Rebel vehicles were spotted moving south of Abeche, where French forces have a base, and about 250 kilometers (155 miles) of the capital N'Djamena, Burkhard said Thursday. France has some 1,250 soldiers based in Chad, a former colony which gained its independence in 1960.