Ukraine Calls for a 'Resolute Response' After Plane Shot Down (continuous)

Poroshenko, who took office after a special election was called to replace ousted pro-Russia President Viktor Yanukovich, declared Sunday a day of mourning, adding that those involved in the attack "will certainly be punished."

"Ukraine needs peace, but terrorists will get a response they deserve," he said.

In another incident, five Ukrainian border guards were killed and seven wounded Saturday morning when their convoy ran into an ambush near Mariupol in the Donetsk region, the border guards service reported in a statement posted on its website. Ukrainian forces retook the industrial port city on the Sea of Azov from separatists on Friday.

During Poroshenko's meeting with military, security and law enforcement chiefs, acting Defense Minister Mykhailo Koval reported that in the previous 24 hours more than 250 pro-Russia gunmen had been killed in the military's operations designed to regain control of areas in eastern Ukraine seized by fighters in the last two months. The separatists in Russian-speaking areas of the east and south are opposed to the new central government in Kiev and in some cases hope to unify with neighboring Russia.