The prisoner release Monday means nearly 100 members of Asaib Ahl al-Haq, or League of the Righteous, have left U.S. custody since late last week.

At least one of the British hostages is believed still be alive.

An envoy for the militant group, Salam al-Maliki, says talks are under way for the release of its leader, Sheikh Qais al-Khazali.

But negotiations are complicated by efforts to seek guarantees about freeing Peter Moore, the sole hostage believed to be living.