SLOVYANSK, Ukraine — From the country’s richest man to citizens under fire, anger and dismay over Ukraine’s eastern turmoil gained strength Tuesday, but pro-Russian rebels who have declared the region independent vowed defiance.

In Kiev, home to the central government that the separatists detest, lawmakers passed a memorandum that guaranteed the status of Russian as Ukraine’s second official language and proposed government decentralization. While the document offered no specifics or time frame, Russia – which long had pressed for both commitments – offered words of guarded welcome.

“If what you are saying is true, this is the development we have been speaking about for the past months,” Russian Deputy Foreign Minister Grigory Karasin was quoted as telling state news agency RIA Novosti.

In Mariupol, an eastern Ukrainian city that suffered fatal clashes this month between protesters and police, workers at a steel mill stopped their labor at noon as a siren blew. They gathered for a speech from the company’s chief condemning the separatist movement known as the Donetsk People’s Republic.

“We are here because Mariupol needs a peaceful sky above us. Tanks and guns have no place in our city,” said millworker Sergey Kulitsh.

The plant is part of the industrial empire of Rinat Akhmetov, regarded as Ukraine’s richest man, who had called for his workers to attend noontime protests.

The tycoon vowed to challenge the insurgents who declared independence last week in the Donetsk and Luhansk regions, home to 6.5 million people.

“No one will frighten us, including those calling themselves a Donetsk People’s Republic,” Akhmetov said in a statement.

Last week, his company organized steelworkers to patrol alongside police in Mariupol. The move forced insurgents to vacate government buildings they had seized in the Black Sea port.

Ukrainian Interior Minister Arsen Avakov hailed Akhmetov’s move as likely to “sweep the terrorist scum away better than any counterterrorist operation.”

One rebel leader in Donetsk, Denis Pushilin, retaliated Tuesday by threatening to nationalize Akhmetov’s businesses over his refusal to pay taxes to the separatists.

Ukraine is holding a presidential election Sunday, which Kiev hopes will unite the country behind a new leader.

Separatists exchanged fire again Tuesday with government forces on the outskirts of Slovyansk – the epicenter of the rebellion against the government – as residents voiced their anger over the fighting.