After a day of punishing air strikes and fierce fighting with pro-Russian separatist gunmen, Ukraine said on Tuesday that it had regained control of the Donetsk airport.
However, dozens of militants were killed in the unprecedented assault by Ukrainian government forces, which continued on Tuesday, according to media reports.
Reuters journalists counted 20 bodies in combat fatigues in one room of a city morgue in Donetsk. Some of the bodies were missing limbs, sign that the government had brought to bear overwhelming firepower against the rebels for the first time.
“From our side, there are more than 50 [dead],” the prime minister of the rebels' self-styled Donetsk People's Republic, Alexander Borodai, told Reuters at the hospital.
Donetsk mayor Oleksandr Lukyanchenko told reporters that two civilians and 38 combatants had died, while rebel leaders suggested that the toll among their ranks could be higher, the French news agency AFP reported.
The government said it suffered no losses in the assault, which began with air strikes hours after Ukrainians overwhelmingly voted to elect a 48-year-old billionaire confectionary magnate Petro Poroshenko as their new president.
At least 100 rebels were killed in Monday's battle for control of the airport in Donetsk, said a pro-Russian separatist who declined to be identified, according to Reuters. Rebel leaders told the AP that the death toll for their forces could rise to up to 100.
“We failed because their numbers were greater than ours several fold. We seized the main airport building, but afterwards they started shelling, firing from jet fighters and helicopters,” the separatist, who was shot in the leg, told Reuters.
Russia calls for halt to offensive
Russian President Vladimir Putin, who has declared Moscow's right to intervene to protect Russian speakers in Ukraine, demanded an immediate halt to the offensive.
Russian Foreign Minister Sergey Lavrov also called for a quick end to the military operation, adding that Russia supports efforts to negotiate a peaceful end to the crisis.
Moscow, however, said it would not consider a visit by Poroshenko for any talks.
Ukraine's First Deputy Prime Minister Vitaly Yarema said the "anti-terrorist operation" in eastern Ukraine would continue until "not a single terrorist remains on the territory of Ukraine."
Emboldened by election
Until now, Ukrainian forces have largely avoided direct assaults on the separatists, in part out of what they say is fear of precipitating an invasion by tens of thousands of Russian troops massed on the border.
But the government in Kyiv appears to have interpreted Poroshenko's big election victory - he won more than 54 percent of the vote in a field of 21 candidates, against 13 percent for his closest challenger - as a mandate for decisive action.
After rebels seized the Donetsk airport on Monday, Ukrainian warplanes and helicopters strafed them from the air and paratroopers were flown in as part of the assault.
Shooting carried on through the night and on Tuesday the road to the airport bore signs of fighting. Heavy machinegun fire could be heard in the distance in mid-morning.
“The airport is completely under control,” Interior Minister Arsen Avakov told journalists in the capital Kyiv. “The adversary suffered heavy losses. We have no losses,” he added.
Borodai, the rebel prime minister, also said the airport was now under government control.
The military strikes mark the first time the government has unleashed the full lethal force of its aircraft and ground troops directly at the Donetsk rebels, a group of local volunteers and shadowy outsiders led by a Muscovite that Kyiv and Western countries say is a Russian military intelligence agent.
The Organization for Security and Cooperation in Europe said on Tuesday it had lost contact with a four-member observer team in the restive Ukrainian city of Donetsk, AFP reported.
Their disappearance comes more than a month after another OSCE team of military observers was captured by pro-Moscow rebels in eastern Ukraine and held in the flashpoint city of Slovyansk for over a week.
OSCE spokesman Michael Bociurkiw said Tuesday that the officials were traveling between cities in eastern Ukraine when they dropped out of contact.
"They were headed eastbound, we know that, between Donetsk city and the border with Luhansk Oblast, and there was some texting going back and forth, and then at around 6 (p.m.) their phones went dead, and from there we didn't hear anything further from them,” Bociurkiw said.
There was no immediate claim of responsibility, but rebel groups have previously kidnapped OSCE monitors in Ukraine.
The OSCE said the four were international members of its Special Monitoring Mission - a Dane, an Estonian, a Turk and a Swiss national, the AFP reported.
Over 1,000 observers from the OSCE and other international bodies had been in Ukraine to monitor Sunday's presidential election.
U.S. President Barack Obama congratulated Ukraine's Poroshenko on his election victory on Tuesday and offered U.S. support as he seeks to unify the country, the White House said in a statement.
Obama stressed the importance of quickly implementing the reforms necessary for Ukraine to bring the country together and to develop a sustainable economy, attractive investment climate, and transparent and accountable government that is responsive to the concerns and aspirations of all Ukrainians, the statement read.
Obama congratulated Poroshenko and offered “the full support of the United States as he seeks to unify and move his country forward.”
The two leaders agreed to continue their conversation during Obama's trip to Europe next week, the White House said.
Some information for this report provided by Reuters, AP and AFP.