Kiev - Three pro-Russian militants died and 13 were wounded when Ukrainian troops repelled an attack on a National Guard base in the Black Sea port of Mariupol, Ukraine's interior minister said on Thursday.
A crowd of around 300 men armed with Molotov cocktails attacked the base, in the south-east part of the country late on Wednesday, Interior Minister Arsen Avakov said in a statement.
He said they were repelled by the National Guard and police forces and 63 people had been arrested as a result of the operation. Most of the attackers were disarmed, he added.
The skirmishes come after the Ukrainian government announced an operation to retake control of Solvyansk and other cities in the restive east.
A well-armed, Russia-backed insurgency has sowed chaos in eastern Ukraine in the past weeks.
On Wednesday, Moscow-backed insurgents seized armoured vehicles and weapons from underequipped Ukrainian government forces and militants have taken control of police stations and administrative buildings in at least 10 towns in the region, including Mariupol near the Russian border.
With tens of thousands of Russian troops deployed along the border with Ukraine, there are fears the Kremlin might use the instability in the predominantly Russian-speaking region as a pretext for seizing more territory beyond its annexation of Crimea last month.
The latest unrest came just hours before diplomats from Ukraine, the US, the European Union and Russia prepared to meet on Thursday for the first time over the burgeoning crisis that threatens to roil the new government in Kiev.
With Ukraine struggling to contain the pro-Russian uprising, the Obama administration has said it is readying additional sanctions against Moscow and a boost in aid for the Ukrainian military in the coming days.