Live Blog: Ukraine In Crisis (Archive)

Still no confirmation of separatists' claim that they shot down a Ukrainian bomber after it hit a target in the rebel-held town of Horlivka, in the Donetsk region.

Ukrainian President Petro Poroshenko has declared a day of mourning for those killed in the deadliest attack on national troops since the pro-Russian uprising began in the country's south and east.

Unofficial reports suggest 49 people -- 40 troops and nine crew members -- perished when a Ukrainian army transport aircraft was struck by a surface-to-air missile overnight as it approached Luhansk airport, where heavily armed separatists control much of the area.

Poroshenko says in his statement that the day of mourning, June 15, marks "a great loss not only for the families of the victims but also for the whole country. Ukraine is in sorrow, but we strongly continue the struggle for peace."

The apparent escalation in fighting comes after weeks of images of Russian gunmen crossing the border and amid fresh allegations by the United States that "separatists in eastern Ukraine have acquired heavy weapons and military equipment from Russia, including Russian tanks and multiple rocket launchers."

"All those involved in the cynical terrorist attack of such magnitude must be punished," says the statement by Poroshenko, who vowed after his election in May and again at his June 7 inauguration that talks in the separatist east and with Moscow were a priority. "Ukraine needs peace. Counterterrorism receives an adequate response."

Reuters and Russian agencies are quoting Russian gas giant Gazprom as saying it is preparing for talks in Kyiv on its gas-pricing dispute with Ukraine. "We are ready to seek compromise, but it is useless to put pressure on us," Gazprom spokesman Sergei Kupriyanov said.

Ukraine has said it is ready to start settling its gas bills if Russia agrees to charge $326 per 1,000 cubic meters of gas for 18 months.

Russia has said its "final price" is $385 per 1,000 cubic meters and threatened to cut off gas supplies to Ukraine if Kyiv does not pay state-controlled Gazprom $1.95 billion by June 16.

via @ChristopherJM

There are a number of reasonable explanations (settings, overwrites, etc.), but some are questioning the timing of a LifeNews post regarding video purporting to show at least one surface-to-air missile being fired and subsequent blasts from the impact of the Ukrainian army transport aircraft near Luhansk.

Separatists claim the Ukrainian air force fired on the rebel-held town of Horlivka, in Donetsk region, killing one person. That report is unconfirmed.