The Boko Haram terrorist group has executed a second humanitarian aid worker of three it kidnapped in March.

It has said the surviving worker, with kidnapped Christian schoolgirl Leah Sharibu, will be slaves for the rest of their lives, according to Christian Solidarity Worldwide.

Midwife Hauwa Mohammed Liman, 25, was working for the International Committee of the Red Cross (ICRC) was seized on March 1, along with fellow ICRC worker and midwife Saifura Husseini Ahmed, 25, and nurse Alice Loksha Ngaddah, a UNICEF employee. Their abduction followed an attack in Rann, Borno state, in which two humanitarian workers from the International Organisation for Migration (IOM), one from the ICRC and another from UNICEF, were murdered.

A video depicting her execution was sent to the Nigerian newspaper The Cable. In a statement, the terrorists said both she and Ms Ahmed were considered apostate as they were deemed to have abandoned their faith by working for the Red Cross: 'For us there is no difference between the Red Cross and UNICEF. If we see them we kill the apostate among them, men or women, and choose to kill or keep the infidels as slaves, men or women.'

They also said that from that day onwards the remaining hostages, Alice Ndaggah, a mother of two, and 15-year-old Leah Sharibu, were their slaves and that 'it is now lawful for us to do whatever we want with them'.

Leah was the only Christian among 110 girls abducted from their school in Dapchi, Yobe state. She has refused to convert to Islam.

Boko Haram released a video on September 18 in which Ms Ahmed, also a mother of two, was made to kneel and then executed with a shot to the back of her head. In the video an unidentified terrorist complained that the Nigerian government had ignored written and audio messages, and described the murder as 'a message of blood'. He also threatened her colleagues and Ms Sharibu with a similar fate if unspecified demands were not met within a month.

Hauwa Mohammed Liman was executed upon the expiry of the terrorists' deadline.

Mervyn Thomas, CSW's chief executive, said: 'Our hearts go out to the family and friends of Hauwa Liman, whose pain is unimaginable. We condemn this cowardly execution in the strongest terms. It is senseless, inhumane and cannot be justified on any grounds, let alone religious ones. Ms Liman merely sought to improve the lives of vulnerable female IDPs, yet her life, like Saifura Ahmed's, was cut short by what is in reality a death cult.

' It is deeply disturbing that Leah Sharibu and Alice Ngaddah remain in the hands of this profoundly nefarious sect. We appeal to the government of Nigeria once again to do everything in its power to expedite the release of Ms Ngaddah, Ms Sharibu and the 112 remaining Chibok girls, and to ensure the armed forces are fully equipped to address this insurgency. We also urge the church worldwide to continue in earnest prayer until all of Boko Haram's captives are set free.'