(http://news.bbcimg.co.uk/media/images/75306000/jpg/_75306515_line976.jpg)
Who are Boko Haram?(http://news.bbcimg.co.uk/media/images/77158000/jpg/_77158275_nigeriacameroon4640814.jpg)
- Founded in 2002
- Initially focused on opposing Western education - Boko Haram means "Western education is forbidden" in the Hausa language
- Launched military operations in 2009 to create an Islamic state
- Thousands killed, mostly in north-eastern Nigeria - but also attacks on police and UN headquarters in capital, Abuja
- Some three million people affected
- Declared terrorist group by US in 2013
Who are Boko Haram? (http://www.theinfostride.com/news/world-africa-13809501)
Profile: Boko Haram leader Abubakar Shekau (http://www.theinfostride.com/news/world-africa-18020349)
(http://news.bbcimg.co.uk/media/images/75306000/jpg/_75306515_line976.jpg) Boko Haram controls several areas, mostly in Borno state where the group was launched, but also in neighbouring Yobe state.
Nigeria's military spokesman Chris Olukolade responded with a statement dismissing the declaration of an Islamic state as "empty".
The video also shows about 20 men in civilian clothes apparently being shot dead.
The BBC's Nathalie Wakam in Cameroon says the situation is worrying for the country's officials, who have called on the international community to help them tackle the threat from Boko Haram.
China, France, the US and UK all sent some military assistance - advisors and help with intelligence - to Nigeria after some 200 schoolgirls were seized from Chibok, near Gwoza, in April.
Source: BBC