SLOVYANSK, Ukraine - At least 14 people were killed and scores were wounded as government forces seeking to win back this eastern Ukrainian city from pro-Russia separatists ran into an ambush Monday set up by the rebel gunmen.

Operations by the Interior Ministry, army, and national guard troops for the last two weeks - often more off than on - erupted in a massive shootout as their armed convoy rolled into Semyonvka, a suburb of Slovyansk. They were met by separatists firing Kalashnikovs, grenade launchers, and large-caliber machine guns.

The gun battle underscored the tough resistance government forces have faced in confronting the rebels - directed, they say, by Moscow - who have seized control in more than a dozen towns and cities in eastern and southern Ukraine.

Witnesses described the scene outside Slovyansk, one of the centers of the rebellion, as harrowing, especially after a gas station exploded in a wall of flame.

"For a moment I lost my hearing as my car was shaken by an explosion behind," said Alexei Sergiyenko, 36, a factory worker who had just refueled his car at the station. "I stopped the car about [110 yards] from the place, ran out, and lay behind it."

Sergiyenko said gunfire continued for about five minutes. When he drove back into town, two armored vehicles carrying more than a dozen gunmen and flying the white flags of the self-proclaimed Donetsk Republic rolled past him toward the battle.

The Interior Ministry said government forces suffered four dead and 30 injured, UNIAN news agency reported. Seven rebels were slain and three were injured, said Vyacheslav Ponomaryov, the self-proclaimed mayor of Slovyansk. In addition, three civilians were killed and 15 were wounded.

"They are using a cunning in-and-out tactic with us, obviously counting that we will soon run out of our manpower, given their blockade of Slovyansk," Ponomaryov said. "But I must boast that a lot of our friends arrived in Slovyansk this weekend to help us fight the fascist junta," the pro-Russia mayor added, hinting at what Ukrainian officials say is the case: that Russians are involved in the conflict.

"We are dealing with a very well-prepared adversary armed with grenade launchers, mortars, and machine guns," Stepan Poltorak, commander of the national guard, said at a briefing near Slovyansk on Friday, a video of which was posted on the Interior Ministry's website. "We tightened our grip around them in the center of the town, but they are not letting us come closer."

Acting Interior Minister Arsen Avakov said at the same briefing that the slow pace of the operation was the result of efforts to spare the lives of civilians.

Avakov also said that a special forces unit was dispatched Monday to Odessa to restore order there. At least 46 people died in the Black Sea port Friday during a clash in which firebombs set ablaze the city's trade union building.

In Kramatorsk, near Slovyansk, a few hundred people attended the funeral Monday for Yulia Izotova, 21, a nurse who was killed two days earlier in a clash between separatists and troops. Among the mourners were dozens of gunmen in masks.