More than 14,600 Afghans and 7,900 Cameroonians are legally in the US under the programme which grants temporary safety.
Trump administration says it needs more time to plan return of man who was mistakenly deported to an El Salvador prison.
Two countries hold talks in bid to avoid confrontation in Syria.
Military head Oligui Nguema is the strongest candidate, but his ties to the old government have led to criticism.