The United Nations on Saturday said Burkina Faso had no grounds for ordering senior U.N. official Barbara Manzi to leave the country and that the doctrine of "persona non grata" could not be applied to her.

Burkina Faso's military government on Friday put out a statement instructing Manzi, appointed U.N. resident coordinator last year, to leave the West African country with immediate effect.

Foreign Minister Olivia Rouamba later accused Manzi of painting a negative picture of the security situation in Burkina Faso, which has been grappling with a violent Islamist insurgency since 2015.

Manzi "predicted chaos in Burkina Faso in the next few months", Rouamba said on national television, alleging she had unilaterally recommended the evacuation of some U.N. staff and their families from the capital Ouagadougou.

"She discredited the country and discouraged potential investors," Rouamba said, noting the government's "big efforts" towards improving security.

The U.N. Secretary-General "learned with regret" about Burkina Faso's decision and expressed "full confidence... in Ms. Manzi's commitment and professionalism", spokesperson Stephane Dujarric said in a statement on Saturday.

"The doctrine of persona non grata does not apply to United Nations officials," he added.

"Only the Secretary-General... has the authority to decide, after careful investigation, with respect to the withdrawal of any United Nations official."

Reuters was not immediately able to verify whether Manzi, an Italian national, was still in Burkina Faso in Saturday.

She had previously told a Reuters reporter that she would be travelling for year-end holidays on Dec. 24.

The U.N. provides some essential services in Burkina Faso, including supplying food to thousands of malnourished children as insecurity has crippled local economies, caused mass hunger, and restricted access for aid organisations.

The country, one of the world's poorest, is battling militants linked to al Qaeda and Islamic State who have killed thousands of civilians.

Nearly two million people have been displaced from jihadist hotbeds in the north and east and reside in makeshift camps, many run by the U.N.

Frustrations over growing insecurity spurred two military takeovers this year. Both the previous and current juntas have made efforts to beef up security in a bid to stem the insurgency, but attacks have continued.

The Secretary-General reiterated the U.N.'s commitment to continue engaging with Burkina Faso's transitional authorities and support the country.