A new video by Boko Haram threatens to kill Nigeria's president and army chief and warns of further destruction, though the Islamic extremists have not mounted a major attack in Nigeria in months.

A preacher in the video says Boko Haram is "even stronger now" and "will destroy what we never destroyed before," according to a translation from the Hausa by Premium Times newspaper.

The video posted on YouTube on Wednesday says it was shot Monday in Nigeria's northeastern Sambisa Forest at prayers marking Eid al-Adha festival. It shows scores of worshipping men, many armed, in a mosque and at an outdoor ceremony.

Boko Haram is in the midst of a power struggle and the video declares allegiance to long-time leader Abubakar Shekau.

The 7-year uprising has killed more than 20,000 people.