Ukraine’s interior minister said Tuesday that 30 pro-Russian insurgents and four government soldiers were killed in fighting in the eastern city of Slovyansk.

Arsen Avakov announced the news on his Facebook page on Tuesday. The fighting has escalated in the eastern city with several gun battles reportedly taking place in different parts of the city Monday. The latest stream of violence belongs to one of the Ukrainian government’s most ambitious efforts to reassert control over the region before scheduled presidential elections on May 25 and a pro-Russian militant referendum on May 11.

According to Avakov, pro-Russian militants are using large-caliber weapons and mortars. There are about 800 insurgents in the region, he said Monday.

In Donetsk, a major city about 75 miles south of Slovyansk, the local airport was closed. On its website, the airport said it was closed due to a government order. It was not clear whether it would reopen on Tuesday. 

On Monday, Acting Ukrainian President Oleksandr Turchynov said he is willing to negotiate with pro-Russian separatists but has also said that talking to "someone who picks up and uses weapons against citizens of Ukraine" would be impossible.

Russia's Foreign Ministry called on Kiev on Monday to "stop the bloodshed, withdraw forces and finally sit down at the negotiating table" and accused the government of "terrorism against their own people" by deploying the military and said a "humanitarian catastrophe" is brewing in the region.

The fighting in Slovyansk comes days after clashes in the southern city of Odessa, where 46 people were killed in rioting and a deadly fire. On Monday, the Ukrainian government said it would be deploying an elite national guard to quell the violence.

“Ukraine is in grave danger of collapsing as a country,” James Goldgeier, dean of the School of International Service at American University in Washington, D.C., told NBC News on Monday. “Any expansion of the unrest is significant.”