Ukraine's parliament is holding an emergency session to discuss the escalating crisis in the east of the country.
Ukrainian media reports say security chiefs on May 6 are expected to brief lawmakers of the Verkhovna Rada behind closed doors on the situation in the east, where pro-Russian forces have seized government buildings and police stations in a string of cities and towns.
Interior Minister Arsen Avakov said 30 pro-Russian militants were killed during an operation mounted by government forces against the rebels in the flashpoint city of Slovyansk.
Avakov said four Ukrainian troops were also killed in fighting around Slovyansk on May 5. A military helicopter was also shot down by the pro-Russian fighters, the third to be shot down since the offensive began last week, though in this case the crew survived.
WATCH: Lavrov: New Talks On Ukraine Would Be Pointless
In Vienna, Russian Foreign Minister Sergei Lavrov said any new international talks on easing Ukrainian tensions should include pro-Russian rebels in the east and south of Ukraine.
Following a Council of Europe foreign ministers' meeting on May 6, Lavrov said he was not against a new round of talks in Geneva but said progress was unlikely unless representatives of the pro-Russian rebels were invited.
He also said "consistent efforts" were being made to make "meaningless" the agreement reached on April 17 in talks in Geneva involving Ukraine, Russia, the United States and the European Union.
That agreement called for the dissolution of all illegal military formations in Ukraine. It also said those occupying buildings should leave them and lay down their arms.
Lavrov also said Ukraine's authorities should pull back the army from eastern regions in order to deescalate tensions. He said it would be "rather unusual" to hold elections in Ukraine while the army is being deployed against the civilian population.
Ukrainian Foreign Minister Andriy Deschytsya rejected the demand that pro-Russian rebels be included in a possible new round of Geneva talks. He demanded instead that Russia stop interfering in Ukraine ahead of the planned May 25 presidential election and set this as a condition before there can be a new round of talks.
The Ukrainian government accuses Russia of engineering the crisis in eastern Ukraine. Avakov has said there were Russians and Chechens among the pro-Russian fighters in Slovyansk.
Moscow denies it has special forces operating in Ukraine's east and accuses the Kyiv government -- which it refuses to recognize -- of "waging war against its own people."
Moscow has also warned of an impending humanitarian crisis in eastern Ukraine and called on Kyiv authorities to stop military operations in the region.
Meanwhile, the Ukrainian government announced it had fired the governor of the Black Sea region of Odesa, where 46 people died in a building fire amid fighting between pro-Russian and pro-Ukrainian activists.
The government had earlier fired the police chief of Odesa over the May 2 violence and also sent an elite national guard force to the city.
Kyiv said the special forces would replace local police who had failed to control pro-Russian activists in Odesa during the weekend.
Amid the escalating unrest, the airport in the eastern city of Donetsk was closed.
A statement published on the Donetsk airport website on May 6 said departing and arriving flights had been suspended by government order.
The government gave no information about the closure.
With reporting by AFP, AP, and UNIAN