The Ukrainian military has launched airstrikes against separatist strongholds in the country's eastern region fol-lowing the shooting down of a transport plane that killed 49 people.

The military on Saturday targeted rebel checkpoints in Luhansk and a military base that had been taken over by armed separatists, in retaliation for the downing of the plane, Al Jazeera reported on Sunday.

Ukraine's President Petro Poroshenko summoned security chiefs for consultations after the plane was hit by an anti-aircraft missile as it came in to land at an airport outside the city of Luhansk, a center of the rebellion in east Ukraine.

"All those involved in cynical acts of terrorism of this magnitude must be punished," he said, declaring Sunday a day of mourning for the nine crew and 40 paratroopers killed.

"For the sake of peace, we will act decisively and purposefully," he said.

Flags were lowered across the crisis-hit nation while television stations inserted an image of a burning candle into their frames after Ukrainian forces suffered the single biggest loss of life in their escalating two-month push to reclaim control of separatist areas of the industrial east.

In a related development, Russian officials lashed out at Ukraine's foreign minister on Sunday after footage showed him using an expletive to describe Russian President Vladimir Putin as he sought to calm angry demonstrators attacking the Russian embassy in Kiev.

Andriy Deshchytsya was filmed by local television being cheered by protesters after telling them "Putin is a prick" in a bid to stop the crowd storming Russia's diplomatic mission on Saturday.

Angry demonstrators smashed the building's windows and overturned diplomatic cars as police looked on after the transport plane was shot down.

United Nations Secretary-General Ban Ki-moon on Saturday condemned in the strongest terms the downing of the Ukrainian airplane.

"The continuing violence in eastern Ukraine - characterized by growing loss of life and a deteriorating humanitarian situation - highlights the need for an immediate cessation of hostilities and a resolution of the crisis through negotiation and dialogue," said a statement issued by Ban's spokesman.

Also on Saturday, US Secretary of State John Kerry called on Russia to end the flow of weapons and support to separatists in Ukraine. In a phone talk with Russian Foreign Minister Sergei Lavrov, Kerry expressed strong concern about events over the last few days in Ukraine, including the transport of heavy weaponry and militants across the border and the shooting down of the Ukrainian transport flight, the US State Department said.

Reuters - AFP - Xinhua