In 1774, the Mamluk governor of the Ottoman province of Iraq, Omar Pasha began meddling in the affairs of his vassal principality of Baban, which since the death of his predecessor Sulayman Abu Layla Pasha in 1762, had fallen more and more under the influence of the Zand governor of Ardalan, Khosrow Khan Bozorg. This made Omar Pasha dismiss the Baban ruler Muhammad Pasha, and appoint Abdolla Pasha as its new ruler. This, and Omar Pasha's seizure of the remnants of Iranian pilgrims who had died during the plague that ravaged Iraq in 1773—and his exaction of payment from Iranian pilgrims to visit the holy Shia places of Najaf and Karbala, gave Karim Khan the "casus belli" to declare war against the Ottomans.