Al Qaeda's affiliate in Yemen -- al Qaeda in the Arabian Peninsula -- strongly rebuked ISIS in a video released Friday, declaring ISIS leader Abu Bakr al-Baghdadi's declaration of an Islamic caliphate to be illegitimate.

The statement, delivered by one of AQAP's top clerics -- Harith bin Ghazi al-Nadhari -- is a significant setback to ISIS efforts to assume leadership of the global jihadist movement a week after groups in Egypt and Libya joined the ISIS fold.

ISIS and al Qaeda's top leadership in Pakistan had a bitter falling out earlier this year, and al Qaeda and ISIS fighters have been fighting each other in Syria, but AQAP had until now stayed above the fray, calling for both sides to reconcile and pool resources to strike the United States.

But when al-Baghdadi declared in an audiotape released last week his Islamic State had expanded to Yemen, as well as other Middle Eastern countries, it was too much for the AQAP leadership to stomach.

By claiming Yemen for his caliphate, al-Baghdadi had called into question the very right of AQAP to exist as a separate and autonomous jihadi group, leaving its leadership no choice but to push back.

"We did not want to talk about the current dispute and the sedition in Syria... however, our brothers in the Islamic State ... surprised us with several steps, including their announcement of the caliphate [and] they announced the expansion of the caliphate in a number of countries which they have have no governance, and considered them to be provinces that belonged to them," al-Nadhari stated, according to a translation by the SITE intelligence group.

"The announcement of the caliphate for all Muslims by our brothers in the Islamic State did not meet the required conditions," al-Nashari argued, because other jihadi groups were not consulted.

The cleric also criticized ISIS for "going too far in interpretations in terms of spilling inviolable blood under the excuse of expanding and spreading the power of the Islamic State."

And in a repudiation of al-Baghdadi's claim to supremacy among jihadis, he reaffirmed the group's pledge of allegiance to al Qaeda leader Ayman al-Zawahiri and Taliban leader Mullah Omar.

In forcing AQAP to publicly choose sides, al-Baghdadi appears to have badly miscalculated. AQAP leader Nasir al Wuhayshi, despite being named the number two of al Qaeda globally by al-Zawahiri last year, had been careful not to weigh in publicly on the dispute between al Qaeda and ISIS, restricting himself only to a poem he released in July praising his Egyptian boss.

In February, the general command of al Qaeda declared it had severed ties with ISIS because of its insubordination and its brutal tactics against fellow Muslims.

By then, Jabhat al Nusra, al Qaeda's affiliate in Syria, and ISIS were already fighting each other in parts of northern Syria. Although U.S airstrikes against both groups in recent weeks have led to ceasefires and some cooperation at the local level against moderate rebel groups, relations have remained tense.

(CNN)