7 March 2015, 20:28 GMT
"Our caliph, God save him, has accepted the pledge of loyalty of our brothers of Boko Haram so we congratulate Muslims and our jihadi brothers in West Africa," spokesman Abu Mohammed al-Adnani said in an audio statement, adding that Boko Haram's pledge had opened a new door for Muslims who could not join IS in Iraq and Syria "to migrate to the land of Islam and fight."
Adnani also issued a threat to Jews and Christians, Reuters reported.
"If you want to save your blood and money and live in safety from our swords… you have two choices: either convert or pay jezyah (tax for non-Muslims under Islamic rule)."
"(Otherwise) you will soon bite your fingers with remorse.
— Rita Katz (@Rita_Katz) March 12, 2015
Boko Haram has killed thousands and kidnapped hundreds in the last six years in its efforts to create an Islamist state in northern Nigeria.