Slovyansk, Ukraine
A Ukrainian security force officer is deployed at a checkpoint that was set on fire and abandoned by pro-Russian separatists near Slovyansk on April 24, 2014. Reuters/Gleb Garanich

Fighting between pro-Russian separatists and the Ukrainian military in the eastern city of Slovyansk broke out again on Monday, killing dozens of people, and a third Ukrainian government helicopter was shot down in the fighting.

According to government statements, the fighting escalated as the Ukrainian military moved to regain control of the eastern part of the country. The Interior ministry said 30 people were killed in the fighting, but it is unclear from the report whether civilians were included in the death toll.

Pro-Russian militants shot down a military Mi-24 attack helicopter in Slovyansk during the fighting on Monday at about 2:30 p.m. local time, the Ministry of Defense said in a statement. The helicopter crashed into a nearby river, and the pilots escaped without injury. It was the third Ukrainian helicopter shot down in the fighting so far. Pro-Russian fighters shot down the first two on May 2 with shoulder-launched anti-aircraft missiles.

The shooting down of military helicopters could signal a new phase in the fighting in Ukraine. The Ministry of Defense released a statement about the first attack last week, which said that the two helicopters were shot down by “man-portable air defense systems” (MANPADS), an acronym for small, lethal missiles, such as the Russian SA-7, that have been used for decades by jihadists in Afghanistan with great effectiveness. It is unclear if the weapons that were used to shoot down the third helicopter on Monday were also MANPADS. The use of MANPADS indicates that the pro-Russian fighters are trained and well-armed.

“A cynic would say MANPADS are quite easy to get if one has a willing sponsor," Austin Long, a professor at Columbia University and a former consultant for the RAND Corporation, said. "The Afghan mujahedin in the 1980s received some of the most advanced MANPADS in the world after the United States decided to supply them. No one, so far as can be told from the outside, has made a similar decision about supplying the Syrian rebels. The United States appears to have discouraged its regional allies from providing MANPADS to the rebels. One could easily imagine that the Russian Federation has made a decision more similar to that of the United States in the 1980s rather than the 2010s.”

MANPADS are surface-to-air missiles that can be carried and fired by an individual. Some of the most frequently used MANPADS can be transported and hidden easily. According to the U.S. State Department, more than 40 civilian aircraft have been hit by MANPADS missiles since the 1970s. It is estimated that more than 1 million MANPADS have been manufactured worldwide since they were first introduced in 1967. In 2002, the United Nations stepped up its efforts to keep the missiles from falling into the wrong hands.

The use of anti-aircraft missiles like MANPADS outside of official military bodies is unusual. For years, the rebels in Syria said they needed anti-aircraft missiles to fight President Bashar al-Assad’s forces. Until a few months ago, Syrian rebels had no way to defend themselves from bombs dropped from government planes and helicopters. Various media reports have indicated that certain Syrian opposition factions may have access to Chinese-made MANPADS.

A U.N. report released in March said shoulder-launched anti-aircraft missiles have been trafficked out of Libya to places like Chad, Mali, Tunisia and Lebanon, and that certain groups, such as rebel fighters in Syria, could benefit from the Libyan anti-aircraft missile trade. It has not been confirmed from where the pro-Russian fighters in Slovyansk received their anti-aircraft missiles, but many suspect the weapons were smuggled in from Russia.

The Ukrainian government announced on Monday that it would close all checkpoints and border crossings between Ukraine and Crimea and set up roadblocks around Kiev to prepare for the Victory Day holiday on Friday. The holiday marks Nazi Germany’s defeat by Soviet forces in World War II, and it is celebrated by the countries that comprised the former Soviet Union.

The government also deployed a special police unit to restore order in the southern port city of Odessa after fighting on Friday left more than 40 dead. Livestream footage of the clashes last week showed police forces intermittently battling protesters throughout the day, but many of the forces did not attempt to control the situation.