KIEV, Ukraine — Ukraine's President Petro Poroshenko vowed to strike back against pro-Russian separatists who shot down a military transport plane early Saturday morning, killing all 49 people aboard and dashing hopes of defusing the conflict any time soon.
Poroshenko announced a national day of mourning after the plane was shot from the sky as it was landing at the airport in Luhansk, an eastern city where separatists have taken over government buildings and declared an independent state. The Ukrainian military holds the city's airport but little else.
The Ukrainian military said rebels used antiaircraft weapons and large-caliber machine guns against the Ilyushin-76 transport plane, which carried 40 paratroopers flying in as part of a routine rotation and a crew of nine. There were no survivors.
Videos filmed after the plane crashed about 1:10 a.m. showed flames lighting up the nighttime horizon. By daylight, debris could be seen strewn over a large area outside the city.
Russian officials did not comment directly on the attack, but they called for an immediate cessation of Ukrainian military operations in the east, to be followed by a dialogue between representatives of the region and the Kiev government.
The deadly attack came as tensions between Moscow and Kiev are rubbing raw. Ukraine claims that Russia has been arming separatists, who have carved out enclaves they want to see become part of Russia.
Last week, Ukraine said three tanks crossed the border into eastern Ukraine, and separatists have acknowledged having possession of them. Though Russia has denied involvement, the U.S. State Department and NATO have said they have proof that military equipment, including tanks and rocket launchers, has crossed the border.
Secretary of State John Kerry told Ukrainian Prime Minister Arseniy Yatsenyuk in a phone call Saturday that the United States is willing to raise the costs for Russia if it does not prevent the flow of arms, according to a senior State Department official.
Poroshenko called a meeting of his national security and defense advisers after the plane was downed and said Ukraine would simultaneously work for peaceful negotiations and go after the perpetrators.
"Ukraine needs peace," he said. "But terrorists will receive an adequate response."