The African Union on Wednesday expressed its "bewilderment" at US President Donald Trump's inclusion of Chad on an updated and open-ended travel ban list issued at the weekend.
In a statement the AU said it had been "perplexed" by the presence of three African countries -- Libya, Somalia and Sudan -- on Trump's original travel ban, and welcomed the removal of Sudan from the new list, issued Sunday.
But it criticised the "unjust" inclusion of Chad, a country with a long history of cooperation with the United States on counter-terrorism.
The AU statement "expressed bewilderment at the imposition of the unjust travel ban on the Republic of Chad, in particular, given its important role in the fight against terrorism in the Lake Chad Basin, Northern Mali, and the Sahel."
Chadian forces, sometimes in close collaboration with the US military, play a leading role in fighting against Nigeria's Boko Haram Islamists.
Chad has suffered Islamist attacks and its capital, N'Djamena, hosts the five-country Multinational Joint Task Force against Boko Haram.
The new travel ban indefinitely blocks citizens of listed countries from entry to the US.
The AU said it shares US concerns over "the threat of terrorism and violent extremism" but that "cooperation and meaningful engagement" were the answer.
"The free and legal movement of people is the foundation of a stronger and mutually enriching relationship between the African continent and the United States," the AU added.
On Sunday, Trump acknowledged Chad as "an important and valuable counterterrorism partner" but added it "does not adequately share public-safety and terrorism-related information" and warned that "several terrorist groups are active within Chad or in the surrounding region."
Iran, North Korea, Syria, Venezuela and Yemen, alongside the three African countries, are subject to the new ban which takes effect on October 18.