Patrols carried out by miners and steelworkers have forced pro-Russian separatists to abandon government buildings in parts of eastern Ukraine after some regions declared independence earlier this week.
"The unarmed patrols in the cities of Mariupol and Makeyevka by employees of companies controlled by Ukrainian billionaire Rinat Akhmetov were intended to restore order a week after fighting broke out for control of Mariupol's police department, according to a spokesman for Akhmetov and official statements from his company."
Akhmetov is thought to be Ukraine's richest person and said in the statement that the independence or absorption of Donetsk into Russia would spell economic catastrophe.
The separatists had declared the "Donetsk People's Republic" in defiance of Kiev after a referendum on Sunday in which those voting overwhelmingly approved independence. However, many appeared to boycott the referendum.
The New York Times says the miners and steelworkers had been deployed in five cities, including Donetsk.
The Times says the patrols were a decisive force in Mariupol, the region's second-largest city, where there was a bloody confrontation between Ukrainian troops and pro-Russian militants last week.
The Associated Press says:
"Since President Viktor Yanukovych's ouster in February, Ukraine's new leadership has reached out to oligarchs for help — appointing them as governors in eastern regions where loyalties to Moscow were strong.
"Ihor Kolomoisky, a metals, banking and media tycoon who was appointed governor of his native region of Dnipropetrovsk, was among those praised for preserving order. Others like industrialist Serhiy Taruta, governor of the Donetsk region, seemed helpless as district after district fell into the insurgents' hands.
"In Mariupol, the first major citizen patrol sponsored by Akhmetov's Metinvest was held Thursday, police spokeswoman Yulia Lafazan said, adding there were now 100 groups of men consisting of two policemen and six to eight steelworkers patrolling Mariupol."
A United Nations report on Friday raised concerns about increasing human rights abuses in eastern Ukraine as armed groups take advantage of the breakdown in law and order, according to the AP.
The Times says it's "still far too early to say the tide [has] turned in eastern Ukraine" but adds that recent events are "a blow to separatists who recently seized control here and in a dozen or so other cities."