A Ukrainian military spokesman says 49 government troops were killed when pro-Russian separatists shot down a cargo plane over the eastern city of Luhansk overnight.
The defence ministry said the Ilyushin-76 transport plane came under anti-aircraft fire over the city of Luhansk.
The plane was carrying troops and military equipment and was about to land at the city\’s airport.
Separately, Moscow has reacted angrily to a violent protest outside its embassy in Kiev, which saw windows smashed and the Russian flag torn down.
Russia\’s foreign ministry accused Ukrainian police of doing nothing to halt the attack, saying it was a "grave violation of Ukraine\’s international obligations", and demanded Kiev take steps to ensure the safety of its diplomats.
Ukrainian defence ministry officials are investigating how the separatists brought down the plane in the east, with reports suggesting the use of three "Stinger-like" missiles or a large-calibre machine-gun.
Everyone on board – nine flight crew and 40 troops – was killed.
In a statement released later on Saturday, Mr Poroshenko said: "Ukraine needs peace. However, the terrorists will receive an adequate response."
Ukrainian officials offered condolences on Saturday to the families of the "killed soldiers", but did not say how many had died in the attack.
A ministry statement said "terrorists" had "cynically" fired a large-calibre machine gun hitting a Ukrainian air force Ilyushin-76 as it was about to land at Luhansk airport, the AFP news agency reported.
Lugansk, which is close to the Russian border, is the main city of one of two eastern regions hit by violence and which has declared its independence from Kiev.
Source – Agencies