DONETSK, Ukraine — Dozens of dead insurgents lay piled in a van outside a morgue Tuesday, and a rebel said more were on the way. Bomb disposal experts disarmed a mortar round lodged in a corpse. A wrecked and blood-soaked truck at the Donetsk airport showed the grisly aftermath of battle.
The fight for eastern Ukraine seems to have taken a ferocious turn, as both sides step up their attacks after the rebellious regions mostly boycotted a presidential election that delivered a decisive winner.
Following a day and night of the heaviest and most sustained assault by Ukrainian government forces to date, the pro-Russia separatist movement finds itself facing an emboldened and resolute national leadership.
With Sunday’s election of billionaire Petro Poroshenko to the presidency, Kiev has received grudging and tentatively positive diplomatic overtures from Russia.
But with evidence that irregulars are continuing to pour into Ukraine from Russia, it remains unclear whether the Kremlin is encouraging fighters whose attack Monday on the Donetsk International Airport showed their increasing aggression.
What is certain is that the Ukrainian government’s anti-insurgent operation has been kicked into a higher gear, with the military unleashing fighter jets, helicopter gunships, and heavy artillery.
Government opponents insist they have taken up arms to defend eastern Ukraine’s Russian-speaking population and have appealed to Moscow for assistance. Kiev condemns the insurgents as ‘‘terrorists’’ bent on tearing the country apart.
Donetsk Mayor Oleksandr Lukyanchenko said 40 people, including two civilians, were killed in fighting after government troops thwarted a rebel attempt to seize the airport, Ukraine’s second-largest.
The bodies of about 30 insurgents were brought Tuesday morning to the Kalinin Hospital morgue, said Leonid Baranov of the self-proclaimed Donetsk People’s Republic. The fighters had been wounded and were being transported to a hospital in a truck when it was shot up by government forces, he said.
Baranov said up to 100 rebels were probably killed in combat, but many bodies had not yet been recovered because they were in areas under government control. His death toll could not be independently confirmed.
‘‘As they are controlling the airport and the fight was there . . . we cannot right now identify exactly how many victims we have,’’ he said, adding that hundreds were also wounded.
After being squeezed out of the airport following hours of intense fighting, insurgents called in several hundred reinforcements. Many were from a unit calling itself the Vostok — or East — Battalion, which Donetsk People’s Republic representatives have said includes combatants from Russia’s North Caucasus.
Later, Ukrainian forces pounded rebel positions, forcing the fighters to retreat in disarray. One overturned truck down the road from the airport showed signs of having struck a tree at high speed.
In an emergency televised address Tuesday, the Donetsk mayor warned residents to stay indoors but also gave assurances that government troops would not push into the city center.
Sporadic gunfire was heard throughout the day around the airport. Many shops and restaurants in Donetsk did not open. One resident, Alexander German, built a sandbag barricade at a crossroad near the overturned truck.
‘‘We’re defending ourselves. They insult us, call us bandits. Do you see weapons on me?’’ he said, displaying his open palms.
Others nearby spoke angrily about the unrest gripping the city — fury that could intensify as what is increasingly looking like an outright military conflict picks up pace.
After Poroshenko claimed victory in the election, hopes were raised of a push for unification. He has vowed to negotiate a peaceful end to the insurgency.
But he also compared the separatists to lawless ‘‘Somali pirates’’ and promised he would stop them from sowing more chaos.
President Obama, who spoke with Poroshenko by phone Tuesday, plans to meet him while in Europe June 3-6, the White House said.