Belgrade, Serbia ? Stefan Markovic slipped and stumbled on Belgrade’s icy streets and cursed both the Russians and the Ukrainians for the bad air he’s breathing.

“Those damned Soviets!” he shouted. “First they destroyed us with their communism. Now they create more misery. They even poisoned the air we breathe.”

A thick cloak of smog choked the capitals of Serbia, Bosnia and Hungary this week as residents and businesses resorted to burning oil, wood and coal — anything that might help them ward off the midwinter chill amid a natural gas dispute between Russia and Ukraine that has cut off supplies to Europe.

Russia invited EU leaders to an energy summit in Moscow today, while Ukraine countered with a pre-emptive strike and convened a meeting with European officials on Friday. No head of state has announced plans to attend the Moscow summit. Ukraine doesn’t oppose a summit but insists it not be in Moscow.

The dispute is now stretching into its third freezing week and the fallout has been severe: at least a dozen confirmed deaths, hundreds of factory shutdowns that could cost billions in lost productivity — and millions of people left to shiver in unheated homes.

As if trembling in subfreezing apartments wasn’t bad enough, a winter storm encased Belgrade in ice. Doctors urged the elderly to stay indoors, warning that their limbs could snap like firewood if they fell.

But bitter cold drove 70-year-old Marija Jovanovic onto the glistening streets.

“I cannot sit at home and shiver,” she said. “Walking keeps me warm.”

In neighboring Bosnia, Serbia became an unlikely savior by sharing some of its own precious gas supplies.

No one missed the irony: Sarajevo froze during the 1992-95 Bosnian war, when Serb forces laying siege to the city shut off its gas, water and electricity.

A week ago, Boris Tadic, Serbia’s Sarajevo-born president, personally intervened and arranged for an emergency gas delivery. But there was a potentially deadly side to the gift. Authorities cautioned that there could be explosions if residents didn’t properly relight heating systems.

Within hours, the first blast dampened Sarajevo’s newfound relief. Five members of the Hadrovic family were injured, including 44-year-old Amy Hadrovic, who suffered burns so severe she had to be brought to a clinic in Germany for skin grafts.

Rabija Ljutovic, 72, wasn’t taking chances.

“I called the gas company and will wait for their team to come and turn this thing on for me,” she said. “No need to blow myself up.”

Across eastern Europe, the crisis hit businesses and factories already pinched by the global recession.

At the usually bustling Munja battery factory in Zagreb, Croatia, there was only eerie silence. Machines were turned off earlier this week after Croatian authorities decided they’d better switch off gas to industry and keep people as warm as possible in homes and schools.

“The workers are at home. Where else would they be?” said Ivan Miloloza, the manager, whose factory is losing 2 million kuna ($370,000) a day. “There is no production, so we sent them home to wait, to rest.”

“We’re like a hotel at peak season that has its fridges full of food, but no stove to cook on,” he said. “It’s worse than during the war.”

Bulgaria, the poorest member of the EU, may have suffered the most. Even before the gas stopped flowing, the 27-nation bloc had frozen millions in funds to pressure the ex-communist country to clean up rampant crime and corruption.

Twice this week, angry Bulgarians demonstrated outside parliament in the capital, Sofia. On Wednesday, dozens were injured, including 14 police officers, when demonstrators hurled stones and bottles.

“I want this government to resign because it cannot guarantee my basic needs — a normal salary, a heated home and safety for my family,” said Ivan Nenov, a 56-year-old Sofia electrician.