DEIR AL-ZOR PROVINCE, Syria, (REUTERS) - Three suicide attackers in women's clothing killed six people leaving the last Islamic State in Iraq and Syria (ISIS) enclave in eastern Syria on Friday (March 15) in simultaneous blasts, the US-backed forces besieging the area said.

The attack appears to be the first to target the many thousands of people who have poured out of the enclave at Baghouz over the five weeks since the Syrian Democratic Forces (SDF) began an offensive there.

People fleeing the area have included surrendering Islamic State fighters, their family members, other supporters of the group, civilians caught up in the conflict and captives of the jihadists.

The SDF and the US-led coalition that supports it have described the remaining ISIS fighters holed up in Baghouz as being the group's most hardened foreign militants.

During the battle for the enclave, they have hidden in tunnels, deployed suicide attackers to strike advancing SDF troops and detonated car bombs.

An SDF spokesman, Mustafa Bali, said the attacks had targeted surrendering family members of Islamic State militants at three crossing points from the enclave into SDF-controlled territory.

Three SDF fighters were slightly injured and it was not yet known if the attackers were women or men in women's clothing, Bali added.

A witness said three women had carried out the attack at the corridor through which people were surrendering to the SDF.

The Syrian Observatory for Human Rights, a war monitoring group based in Britain, said two women had carried out suicide blasts.