BAMAKO (Reuters) - Mali s President Ibrahim Boubacar Keita, head of a group of five countries in Africa s Sahel region, has asked the United States to remove a travel ban on Chadian nationals, saying that a failure to do so could affect Chad s security commitments. Security analysts expressed surprise when Chad, a key U.S. security partner since the Cold War, was named last week alongside North Korea and Venezuela as part of an eight-country the travel ban. Chad s army acts as a bulwark against local and regional armed movements and played a critical role in pushing back troops from jihadist group Boko Haram when they made a bid to expand beyond northeastern Nigeria in 2015. Its troops continue to hold front-line positions in unstable north Mali where jihadists ousted government authorities five years ago. As recently as February, Chad, also a key French ally, hosted a U.S. military training exercise for special forces as part of a broader strategy to empower regional troops such as the G5 Sahel security bloc consisting of Chad, Mali, Niger, Mauritania and Burkina Faso.    The president of the G5 thinks this decision could affect the commitment of Chad, which has until now shown itself to be a key partner in the fight against terrorism in the G5 Sahel and beyond,  said Keita in a statement sent to journalists late on Wednesday.  The president...calls on the authorities to favorably re-examine the matter by lifting the sanctions against Chad,  he added. Chadian officials expressed surprised at the decision earlier this week, calling it  incomprehensible .  The new U.S. measures, which have no end-date, help fulfill a campaign promise President Donald Trump made to tighten U.S. immigration procedures and align with his  America First  foreign policy vision. The White House says the restrictions are the consequences for countries not meeting new requirements for vetting immigrants and issuing visas. 