Ukrainian government forces fought gun battles Monday with pro-Russian militia in the separatist-controlled eastern Ukrainian city of Slovyansk

Russia's Interfax news agency quoted a separatist source in Slovyansk as saying "many" pro-Russian militants, possibly "more than 20," had been killed in the fighting. Ukraine's Interior Ministry reported four paramilitary police had died in the battle. The Defense Ministry reported a Ukrainian armed forces Mi-24 helicopter was shot down over Slovyansk. but the pilots survived.

Local media reports Ukrainian forces recaptured a television tower outside of Slovyansk.

A Russian Foreign Ministry statement called for Ukraine's government to "end the bloodshed, withdraw the troops" and sit down at the negotiating table "to start a normal dialogue on ways to resolve the political crisis."

Referring to the authorities in Kyiv as "organizers of terror against their own people," the ministry claimed eastern Ukrainian towns encircled by government forces are facing a "humanitarian disaster" due to a lack of medical supplies and disruptions of food supplies.

On Sunday in the southern city of Odessa, pro-Russian protesters stormed a police station and gained the release of some activists arrested two days earlier. The protesters used a battering ram on one entrance before pushing their way in through a garage. Authorities freed more than 60 of the 150 people arrested during clashes that led to a fire which killed 42 mostly pro-Russian activists.

Ukraine's interim Prime Minister Arseniy Yatsenyuk visited the port city Sunday, declaring Russia is seeking to destroy Ukraine by engineering clashes in eastern Ukraine and now Odessa. He accused Moscow of engaging in "well-planned provocation" against the interim Kyiv government.

Ukraine says it will continue pressing its military offensive against pro-Russian separatists in eastern Ukraine, while the Kremlin reported receiving thousands of calls for help from the region's Russian-speaking citizenry.

In Moscow, a Kremlin spokesman (Dmitri Peskov) said Russian President Vladimir Putin had not yet decided how to respond to the offensive, or to the deaths in Odessa.

Russia has at least 40,000 troops and armor massed on its border with Ukraine, and the Kremlin says it reserves the right to enter the country to protect ethnic Russians.