New rebel assault deepens Ukraine divide

The insurgency dividing Ukraine has worsened, with militants hurling petrol bombs seizing a key building in the eastern city of Donetsk, as mass pro-Russia rallies were held there and in annexed Crimea.

Kiev's Western-backed government has already admitted its security forces are "helpless" to halt the rebellion it blames on Moscow from spreading across more than a dozen eastern towns and cities.

It has ordered out a Russian diplomat arrested for espionage, risking a tit-for-tat response from Russia.

As fears mounted of the ex-Soviet republic disintegrating, Germany stepped up its appeal to Russian President Vladimir Putin to help free seven OSCE inspectors held in the town of Slavyansk by the rebels - four Germans, a Pole, a Dane and a Czech.

In Donetsk, a mob of around 300 pro-Russian militants throwing Molotov cocktails and bricks stormed the prosecutor's office, beating up outnumbered riot police and stealing their arms and shields while yelling "fascists!"

Once inside, they smashed doors and carried off official photos and Ukrainian national symbols to be burned. The insurgents already held the regional administration building and the city hall in Donetsk.

The assault occurred while 10,000 people in the city marched in opposition to the Kiev government and in favour of closer ties to Russia.

The rally evolved from a traditional International Labour Day march.

In Crimea, the Ukrainian peninsula Russia annexed in March, some 60,000 people marched in the main city of Simferopol to hail Putin bringing them under Moscow's governance, an AFP journalist saw.

Meanwhile, 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 Organisation for Security and Cooperation (OSCE) in Europe dragged on.

In a phone call to Putin, German Chancellor Angela Merkel asked for help to have the OSCE team released.

The unrest in Ukraine, which started with peaceful demonstrations in Kiev against former president Viktor Yanukovych, has rapidly spiralled into one of the worst geopolitical crises in years.