Ukrainian troops launched a dawn raid on this rebel stronghold on Friday, taking several checkpoints around the city but meeting heavy resistance from pro-Russian separatists, who shot down two helicopters, killing two crew members.
Interior Minister Arsen Avakov said the army had attacked at 4:30 a.m. local time and come under heavy fire from what he called “terrorists” and “professional mercenaries,” as it attempted to take the city.
“Against Ukraine’s special forces, terrorists used heavy fire, including grenade launchers and anti-aircraft rocket launchers,” he posted on his Facebook page. “It is the real battle with professional mercenaries.”
Avakov said the separatists were firing from residential apartment buildings because they knew the army was under order not to fire at such buildings.


He said the army had taken control of nine checkpoints around the city, although some remained in rebel hands, according to a Washington Post correspondent in the area. Ukrainian troops in armored personnel carriers were stationed on roads leading into Slovyansk, although fighting seemed to have subsided by late morning.
Ukraine’s defense ministry said two troops had been killed when the helicopters were shot down.
Vyacheslav Ponomarev, the insurgency-appointed mayor of Slovyansk, said rebels had shot down two helicopters, killing one pilot and capturing the other, according to the Associated Press.

The official spokesman for the military wing of the pro-Russian forces, who will give only his first name, Vladislav, said fighting had broken out at several points around the city, and that Ukrainian troops had made incursions into the city itself, AP reported.
At one burning barricade manned by rebels, a fighter who gave his name as Thunder said he had two children and a pregnant wife at home. “I believe the Russian army will be here soon,” he said. “It is time.”
A spokesman for Russian President Vladimir Putin on Friday called the Ukrainian military efforts a “punitive operation,” and said that it was “effectively destroying all hope for the viability of the Geneva agreements” reached on April 17 that were supposed to deescalate the conflict.

The acting Ukrainian government’s actions are “criminal,” Dmitri Peskov, the spokesman, told the Interfax newswire service.
Putin on Thursday sent a special envoy, Vladimir Lukin, to eastern Ukraine to negotiate with pro-Russian separatists who have taken seven international observers hostage, Peskov said. Lukin, Russia’s human rights commissioner, was also Putin’s special envoy to Kiev in February during negotiations prior to then-Ukrainian President Victor Yanukovich’s flight from office.

Tens of thousands of Russian troops have massed at the Ukrainian border, and Russia says it reserves the right to intervene to protect ethnic Russians. Ukraine accuses Russia of financing and arming the separatists, who have seized government buildings across the east of the country and have vowed to hold a referendum on independence on May 11. Russia denies the charge.
Residents of Slovyansk used tires, sandbags and logs to barricade their neighborhoods, and some complained that the Ukrainian army was endangering their lives.
“We should be evacuated, but Kiev thinks of us as terrorists,” said Natalye Botte, a 26-year-old woman who left her home to visit a local kiosk and find out what was happening. “They fly above our heads shooting all day, but there is an orphanage here full of kids, and we have children at home.”

She said she had heard shooting between 4 a.m. and 7 a.m. local time, and two loud explosions, adding that her 2-year-old girl had been scared and unable to sleep. A nearby checkpoint was now in control of the Ukrainian army.
Ukraine’s internal security service accused separatist leaders of ordering their fighters to collect civilians at checkpoints and in buildings to be used as “human shields.”
“The militants also fired at the helicopter of Ministry of Emergency, which arrived on the scene with a team of doctors to provide assistance and evacuation, and wounded one of the doctors,” the security service said in a statement.

Ukraine’s acting president said this week that police were “helpless” to prevent pro-Russian separatists from taking control of large parts of eastern Ukraine. Although the Kiev government announced it had launched an “anti-terrorist” operation in early April, it has been slow to act till now, partly for fear of provoking a Russian intervention in response.

Rebels in Slovyansk have taken several hostages, including journalists and members of a European security monitoring organization. Interior Minister Avakov said the objective of Friday’s operation was to free the hostages, force rebels to lay down their arms, release administrative buildings from their control, and restore the normal functioning of the city administration.