N'Djamena - A US government delegation is visiting Chad, one of six mainly-Muslim countries affected by President Donald Trump's travel ban, in order to assess passport security, a foreign ministry official said on Thursday.The Department of Homeland Security team "has been in Chad for the past week" to evaluate "relative weaknesses" in Chadian passports, said the official, speaking on condition of anonymity."Their concern is that the Chadian passport is not biometric, even though it is secure," the source said. "Their report will determine whether the measure (travel ban) affecting Chad will be lifted."Chad features alongside Iran, Libya, Somalia, Syria and Yemen on the list of mainly Muslim countries whose citizens are banned from travelling to the United States. Trump says the restriction is vital to protect the United States from terrorists.Critics, though, say the measure is ineffective and also Islamophobic, claiming it targets those countries in order to meet a campaign pledge by the US president. North Korea and Venezuela are also on the list.On September 27, the African Union expressed "bewilderment" at Chad's inclusion on the list, describing it as "unjust" for a country that has a long history of cooperation with the United States on counter-terrorism.Chad is playing a frontline role in fighting jihadists in the Sahel, deploying troops in two multinational forces and in the UN peacekeeping force in Mali. Its forces have also been carrying out exercises with US troops.Trump in September acknowledged Chad to be "an important and valuable counterterrorism partner" but said it "does not adequately share public-safety and terrorism-related information.""Several terrorist groups are active within Chad or in the surrounding region," he maintained.