MARIUPOL, Ukraine -- In what could represent a decisive turning point in the Ukrainian conflict and a setback for Russia, thousands of steelworkers fanned out Thursday over the southeastern city of Mariupol, establishing control over the streets and routing the pro-Kremlin militants who seized control several weeks ago.
By late Thursday, miners and steelworkers had deployed in at least five cities, including the regional capital, Donetsk, though they had not yet become the dominant force there that they are in Mariupol, the region's second-largest city and the site just last week of bloody confrontations between Ukrainian troops and pro-Russian militants.
The workers are employees of Rinat Akhmetov, Ukraine's richest man and a recent convert to the side of Ukrainian unity, who on Wednesday issued a statement rejecting the separatist cause of the self-styled Donetsk People's Republic but endorsing greater local autonomy. His decision to throw his weight fully behind the interim government in Kiev could inflict a body blow to the separatists, already reeling from Russian President Vladimir Putin's withdrawal of full-throated support last week.
Wearing only their protective clothing and hard-hats, the workers said they were "outside politics" and just trying to establish order.
Faced with waves of steelworkers joined by police, the pro-Russian activists have melted away, as has any sign of the Donetsk People's Republic or its representatives. Backhoes and dump trucks from the steelworkers' factory dismantled all the barricades, without resistance from either demonstrators or pro-Russian militants.
Metinvest and DTEK, the two subsidiaries in metals and mining of Mr. Akhmetov's company, System Capital Management, together employ 280,000 people in eastern Ukraine, forming an important and possibly decisive force in the region. They have a history of political activism stretching back to miners strikes that helped bring down the Soviet Union. In this conflict, they had not previously signaled their allegiance to one side or the other.
It was still too early to ascertain whether the separatists would regroup to resist the industrial workers, though none were to be found Thursday in and around Mariupol, not even in the public administration building they had been occupying.
"We have to bring order to the city," steelworker Alexei Gorlov said of his motivation for joining one of the unpaid and voluntary patrols organized at the Ilych Steel Works. Groups of six or so steelworkers accompany two policemen on the patrols. "People organize themselves," he said. "In times of troubles, that is how it works."
Workers from another mill, Azov Steel, took one side of the city, while the Ilych factory took the other. Both groups were trying to persuade longshoremen to patrol the port, Mr. Gorlov said.
The two steel mills fly Ukrainian flags outside their headquarters, though, like so much else in Ukraine, the lines of loyalty were muddled. At least a portion of the city's police had mutinied last Friday, leading to a shootout with the Ukrainian national guard, which left at least seven people dead.
Ilych Steel chief executive Yuri Zinchenko is leading the steelworker patrols in the city. He said the company had remained on the sidelines as long as possible, while tacitly supporting unity with Ukraine by conveying to workers that a separatist victory would close export markets in Europe, devastating the factory and the town.
The Ilych Steel Works, a grimy scene of mid-20th century industrial sprawl, is one of Ukraine's most important factories, producing 5 million tons of slab steel a year. About 50,000 people work in the steel industry in Mariupol, a city of 460,000. So far, 18,000 steelworkers have signed up for the patrols, Metinvest executives say.
Mr. Akhmetov's statement spelled out the daunting problems for the regional economy should the Donetsk People's Republic win its struggle with the Kiev government.
"Nobody in the world will recognize it," he said in a video recording. "The structure of our economy is coal, industry, metallurgy, energy, machine works, chemicals and agriculture and all the enterprises tied to these sectors. We will come under huge sanctions, we will not sell our products, cannot produce. This means the stopping of factories; this means unemployment; this means poverty."
Russia itself exports steel, so it has never been a significant market for the region's output.