Ukrainian troops have tightened a security cordon around a major insurgent-held eastern city, but pro-Russia militia acted with impunity elsewhere in the turbulent region bordering Russia, surrounding a major Interior Ministry base.
Thirty pro-Russia insurgents and four government troops were killed yesterday in operations against anti-government forces around the city of Slovyansk, Ukraine's interior minister said.
Rebels said 10 people - fighters and civilians - were killed by Ukrainian troops. They would not elaborate and there was no immediate way to reconcile the figures.
Gun battles around the city of 125,000 were the interim Kiev government's most ambitious effort to date to quell weeks of unrest in Ukraine's mainly Russian-speaking east.
In the south west, authorities attempted to reassert control over the key Black Sea region of Odessa today by appointing a new governor.
This nation of 46 million is facing its worst crisis in decades after its Moscow-leaning president, whose base was in the east, fled to Russia in February following months of protests.
Ukraine's eastern regions, where armed insurgents have seized dozens of government buildings and police stations in recent weeks, are at odds with western and central Ukraine, which seek closer ties with Europe and largely back the government in Kiev.
Interior minister Arsen Avakov gave the death toll on his Facebook page, adding that 20 government troops were injured during fighting in Slovyansk. He said about 800 pro-Russia forces in and around Slovyansk were deploying large-calibre weapons and mortars.
By this morning, Ukrainian forces had taken hold of a key checkpoint north of the city, dealing a blow to insurgent lines of communication.
In Donetsk, a major city 75 miles south of Slovyansk, the airport was closed during the day to international flights following a government order but reopened later.
In the afternoon, about 30 pro-Russia militants armed with automatic rifles and grenade launchers surrounded an Interior Ministry base in Donetsk, demanding that the troops inside not join any government operations against pro-Russia forces.
While it was unclear whether they would attack, besieging a government forces base marked a new offensive by the militants, who had previously focused on seizing police stations and government buildings.
In the south west, Kiev authorities announced they were firing the acting governor in Odessa and replacing him with member of parliament, Ihor Palytsya. Odessa's police chief was also fired over the weekend.
The move over the predominantly Russian-speaking region came after 46 people died on Friday, many in a building fire, after a pro-Ukraine march turned into a melee of fighting.
The concern that Odessa could be the next region to fall to pro-Russia forces - particularly after 67 people detained in Friday's rioting were released by police on Sunday under pressure from an angry crowd - has sparked concern in Kiev.
Opposing sides of the Ukraine conflict have traded bitter recriminations over the Odessa deaths. As residents gathered to lay flowers near the building, they remained confused about what caused the fire and suspicious of the police forces who for whatever reason did not stop the bloodshed.
Those who gathered to commemorate the victims, at least 15 of whom were buried today, fell in both pro-Ukraine and pro-Russian camps. But most people placed responsibility for what happened on the police for standing aside during the violence and for later releasing the pro-Russia activists.
The central government attempted to boost confidence by sending in an elite national guard unit, which could be seen patrolling the streets of Odessa.
The goals of the pro-Russian insurgency are ostensibly broader powers of autonomy for the region, but some insurgents do favour separatism or even joining Russia.
Leaders of the anti-government movement say they plan to hold a referendum on autonomy for eastern regions on Sunday, although no visible preparations for the vote have been seen.
Russia has put the blame for the unrest squarely on the interim government in Kiev. During a meeting in Vienna with the Council of Europe today, Russian foreign minister Sergey Lavrov demanded that the Ukrainian government end its armed assaults on rebel strongholds. He said he was open to another round of international talks to ease the crisis, but only if pro-Russia rebels were included.
"Those who protest ... want their voices heard," he told reporters. "They want to have an equal voice when it comes to deciding the fate of their own country."
His Ukrainian counterpart rejected the proposal, saying the Kiev government already represents all the people of Ukraine.
Ukrainian authorities have blamed Moscow for fomenting the unrest in the east, saying it is an attempt to derail Ukraine's May 25 presidential election. Mr Lavrov repeated Moscow's claims that violence in Ukraine proved the country was not ready for a vote, and that a constitution allowing for greater federalisation should come before a presidential election.
Russia, Ukraine and European and US leaders met in Geneva on April 17 and signed a deal calling for the dissolution of all illegal military formations in Ukraine. But the sides quickly accused each other of violating the agreement, which has done little to mitigate the turmoil in the country's east.