Ukraine's President Petro Poroshenko has resigned Ihor Kolomoisky - the billionaire governor of the key industrial region of Dnipropetrovsk. In a statement released early on Wednesday, Poroshenko's office named Valentyn Reznichenko as the new acting governor of the Dnipropetrovsk region.
It also quoted the president as saying during the talks with Kolomoisky that the region - a centre of heavy industry - should remain "a bastion of Ukraine in the east and protect the peace".
Kolomoisky - who is estimated to be worth more than $2bn (£1.3bn) - has been widely credited with helping bring order in Dnipropetrovsk and halt the advance of pro-Russian rebels further to the east.
He is also financing a number of Ukrainian battalions fighting the separatists in the Donetsk and Luhansk region.
His dismissal comes days after armed men suspected of acting on orders from the oligarch briefly seized the headquarters of the Ukrnafta energy company, in which the tycoon has a 42% stake and its subsidiary UkrTransNafta.
Earlier, Ukraine's parliament had approved amendments to a law on state-owned companies that experts said effectively removed Kolomoisky's control over Ukrnafta.