At least 12,000 Nigerian women and girls are receiving antenatal and psychological care after being raped by terror group Boko Haram (who now wish to be known as Iswap).

Some of the former captives became pregnant as a result of the sexual violence and most of them suffer from depression from the abuse they were subjected to during their captivity, according to a report by the Daily Independent.

Those who were rescued or managed to escape are receiving medical attention from donors and volunteer bodies, who are calling for the Nigerian government to provide more assistance.

"Security of lives of the displaced persons and the volunteers is very crucial and there are increasing fears that the insurgents may not be happy these women are being looked after and may try to attack the camps," a source told the newspaper.

The news followed a statement by the UN Population Fund warning that at least 214 girls abducted by the insurgents and freed by the Nigerian army in May were "visibly pregnant".

In April, a report by the UN warned that groups such as Boko Haram use rape as a weapon of war.

In a separate report, the UN Children's Fund warned that some 800,000 children have been displaced due to violence by Boko Haram. Many of them have been separated from their families and are subjected to abuse such as rape and forced marriage. Some of them are also being used by the terrorists as combatants and for suicide bomb missions.

Battle against Boko Haram

Boko Haram Nigeria

Who are Nigeria's Boko Haram terrorists?

Boko Haram fights against Western influence in Nigeria and aims to impose its version of Sharia law on the country. The group declared an Islamic caliphate in Gwoza, along the Cameroon border, in August 2014.

Boko Haram has raided several cities in the north of the country in a bid to take control of more land.

Three states − Adamawa, Borno and Yobe − have been under a state of emergency since May 2013, due to Boko Haram's attacks.(Photo: Reuters)

Newly elected President Muhammadu Buhari, a former military general and member of the All Progressive Congress party, vowed to end Boko Haram's insurgence and said the country would do everything it could to find the 220 girls abducted by the terrorists from Borno's Chibok village in April 2014.

The Nigerian government is being aided by mercenaries and troops from neighbouring countries Chad, Benin, Niger and Cameroon in its offensive and has scored some successes since the military co-operation started in February.

The US announced it would send military trainers to help the Nigerian army improve its intelligence gathering and logistics.

During a visit to Chad on 3 June, Buhari renewed his commitment to fight the group, which has killed thousands of people since its insurgence started in 2009.

More about Boko Haram