"Let us be clear: their behavior was and still is totally unacceptable," Oxfam said in a statement.
The White House’s decision to penalize a key counterterrorism partner in Africa may already be having negative consequences.
A special tribunal set up in 2013 found him guilty of having ordered the arrest, torture and killing of thousands of Chadians.
The president has been prominent in fighting Boko Haram in West Africa.
The impoverished Central African country, threatened by Boko Haram, goes to the polls in April.
Approximately 90 U.S. military personnel have already arrived in Cameroon, the White House says.
The countries will receive support that builds on the training and military equipment the U.S. has already supplied.
34 people were killed in twin suicide bombings on police targets on Monday
The government blamed the attacks on the Nigerian militant group.
Two hundred vehicles transporting troops have entered northeastern Nigeria to take on the Islamist militants.
The fighting took place where Chad has sent hundreds of troops to help Niger take on Boko Haram.
Nigeria’s military has reportedly agreed a truce with Boko Haram, in a deal that may also see the release of 200 schoolgirls taken hostage by the Islamist group