The foreign ministers of Russia and Ukraine met briefly on the sidelines of a Council of Europe conference in Vienna, Austria's foreign ministry said on Tuesday, to discuss ways to defuse the situation in Ukraine.

"There was a short greeting. They spoke briefly, but not by themselves," a ministry spokesman said of the meeting between Russian Foreign Minister Sergei Lavrov and Ukrainian Acting Foreign Minister Andriy Deshchytsia.

The meeting came late on Monday, after Ukrainian troops had fought pitched gun battles with pro-Russian militias occupying Slovyansk, and the government sent an elite national guard unit to the southern port city of Odessa as Kyiv scrambled to bring much of the country back under the capital’s control.

The Ukrainian Interior Ministry said four officers have been killed and another 30 soldiers injured in the fighting. Gunfire and multiple explosions were heard in and around Slovyansk, a city of 125,000 people that has become the focus of the armed insurgency against the new interim government in Kyiv.

Near Slovyansk on Monday, a Ukrainian military helicopter was shot down, but the pilots survived, Ukraine's Defense Ministry said.

The helicopter, an Mi-24, which came under fire from a heavy machine gun, crashed into a river. The ministry said in a statement its crew members were evacuated to a nearby camp but did not give any details of their conditions. At least three other helicopters have been shot down by pro-Russian armed groups since uprisings began in eastern parts of Ukraine early this year.

Interior Minister Arsen Avakov said on his agency's website that pro-Russian forces were deploying large-caliber weapons and mortars in the eastern region and that there were wounded on both sides.

Government troops were facing about 800 insurgents, he said.

A pro-Russian militia spokesman in Slovyansk said an unspecified number of people had been killed and wounded in the clashes, including a 20-year-old woman killed by a stray bullet.

Both sides indicated that fighting was taking place at several sites around the city.

The tensions in Ukraine also raised concerns in neighboring Moldova, another former Soviet republic, where the government said late Monday it had put its borders on alert.

Moldova's breakaway Trans-Dniester region, located just northwest of Odessa and home to 1,500 Russian troops, is supported by Moscow, and many of its residents sympathize with the pro-Russia insurgency.