Boko Haram leader Abubakar Shekau has denied reports of a ceasefire and insisted that the militant group will not negotiate.

There had been reports in the media that a ceasefire had been brokered by the Nigerian army and that the more than 200 schoolgirls abducted by Boko Haram six months were soon to be freed.

The schoolgirls were abducted by the terrorist group from their school in the village of Chibok in Borno state, north-eastern Nigeria in April.

Boko Haram's actions were condemned internationally and a social media campaign, "Bring Back Our Girls", went global but in the end freeing the girls has proved extremely difficult, despite the involvement of several countries.

Only a few dozen girls have managed to escape and the fate of the rest remains uncertain.

In a video message released on Friday, Shekau categorically denied reports of a ceasefire and said the abducted girls had converted to Islam and been married off, the BBC reports.

"We have not made ceasefire with anyone. We did not negotiate with anyone. It's a lie," he said.

"We will not negotiate. What is our business with negotiation? Allah said we should not."

Human Rights Watch said in a 63-page report last week that forced marriage and conversion was common in Boko Haram's treatment of the women and girls it has abducted.

The report was based on interviews with over 40 witnesses and victims of Boko Haram abductions in Borno, Yobe and Adamawa states, including some of the Chibok schoolgirls who had escaped.

In the report, Human Rights Watch was critical of the Nigerian government for failing to prevent abductions and do enough to support those who manage to escape their captivity.

The Nigerian government was also criticised for failing to bring the perpetrators to justice, and Human Rights Watch warned that Boko Haram had only been "emboldened" to carry out more abductions because of the "relative ease" with which they had seized the Chibok schoolgirls.