Pro-Russian militants yesterday unleashed fresh violence in east Ukraine, storming yet another public building and further fuelling fears that the ex-Soviet republic could disintegrate.
The violence in the city of Donetsk confirmed the separatists' expanding grip in eastern Ukraine, where they hold more than a dozen towns and cities.
Kiev admits it is powerless to halt their advance. Germany, meanwhile, asked Russian President Vladimir Putin to help free a team of international inspectors with the Organisation for Security and Co-operation in Europe (OSCE) held by rebels.
And in Moscow, in a show of the patriotic fervour sweeping the country, 100,000 workers paraded on Red Square for the first time since the 1991 break-up of the Soviet Union.
The parade was technically in honour of International Labour Day, but the banners declaring "Putin is right" and "Let's support the decisions of our president" made it more a victory march for the Russian leader and show of approval for his policies on Ukraine.
By contrast, the May Day march in Kiev - where the government is backed by the West in the showdown with Moscow - was dispirited, attended by a mere 2,000 people.
One participant, a 51-year-old unemployed woman who gave her name as Zhanna, said: "Why do others quietly steal our land? Why does Russia do it, as well as the Ukrainian oligarchs? I am not against Russia, I don't care about what authority will be here, but they should give us a normal life."
In Donetsk, a pro-Russia rally degenerated into a savage attack against a public building defended by outnumbered riot police.
A mob of about 300 militants hurling rocks attacked the city's prosecutor's office, leaving at least four officers wounded.
In Crimea, the Ukrainian peninsula Russia annexed in March, about 60,000 people marched in the main city of Simferopol to praise Putin for bringing them under Moscow's governance.
Putin and his prime minister, Dmitry Medvedev, are reportedly due to make a triumphant visit to the territory late next week.
In the eastern Ukrainian town of Slavyansk, near Donetsk, a near week-long stalemate over the fate of seven detained European military inspectors with the OSCE dragged on.
Rebels in the town have been saying for three days that the inspectors, grabbed last week, were about to be freed after negotiations involving a prisoner swap.
But yesterday, the militants instead said they had exchanged two of three Ukrainian commandos captured separately for some of their colleagues taken prisoner by Kiev, reported the Interfax news agency. There was no immediate confirmation from Ukrainian authorities and the condition of all three men was unknown.
They were last seen on Russian state television cuffed to chairs, their eyes bound by tape and stripped to their underwear. They had been badly beaten.
In a phone call to Putin, German Chancellor Angela Merkel asked for help to have the European OSCE members released.
"The chancellor reminded President Putin of Russia's responsibilities as an OSCE member and called on him to use his influence," Merkel's spokesman said.
The Kremlin said both leaders emphasised the "mediating potential of the OSCE" in calming the crisis in Ukraine.
Meanwhile, Putin reiterated his call for Kiev to end its military operation designed to stop the pro-Russian rebels from seizing more towns.
The West believes Putin is pulling the strings in the insurgency, dismissing his denials that Russian forces are covertly leading rebel assaults.
This week, the US, the EU, Japan and Canada imposed sanctions on powerful Russian individuals and firms as punishment for what is seen as continuing interference by Moscow.
Russia has reacted angrily, but said it would not retaliate in kind at this time.