A Soviet-designed Su-25 jet aircraft crashed in southeastern Ukraine on Wednesday during a training exercise, killing its pilot, the Ukrainian military said.
The incident took place at around 0800 GMT in the Zaporizhya region, about 450 kilometers (280 miles) from Kyiv, a defense ministry spokesman said, without specifying the cause of the crash. Ukraine's military has operated a fleet of about 50 of the Su-25 "Grach" single-seat, twin-engine jets.
It is not known how many are still in active service, with some reported shot down by pro-Russian separatists during the country's 16-month conflict.
Also Wednesday, Ukraine's military and pro-Russian separatists accused each other on Wednesday of escalating violence in eastern Ukraine in defiance of a cease-fire deal, as Ukraine reported one of its soldiers killed in a direct attack.
The guns have been mostly silent since early September, prompting both sides to extend a pullback of lighter weapons, but an increase in cease-fire violations over the past two weeks has underscored the fragility of the peace process.
Renewed violence would also make it less likely that the European Union lifts sanctions against Russia based on a review before the end of the year, though Russia has repeatedly denied it is backing the rebels in east Ukraine.
"Separatists have been making direct attacks on our positions and this is an escalation of the conflict. This is ... targeted attacks and shelling," Ukrainian military spokesman Andriy Lysenko said by phone.
"The reason might be that there is an upcoming G20 summit and the separatists traditionally complicate the situation on the eve of such meetings," he said.
Earlier the military said separatist rebels had violated the cease-fire 21 times in the past 24 hours, prompting government troops to fire back in response.
One Ukrainian soldier was killed in a rebel attack from small arms and grenade launchers near the frontline village of Hranitne, around 70 kilometres (44 miles) south of separatist-held Donetsk city.
This is the first Ukrainian military death in active combat this month.
Meanwhile separatist officials said Ukrainian troops had fired small arms and mortars, noting particular hotspots near Donetsk airport and around the rebel-held town of Horlivka, rebel news agency DAN reported.
They also accused Ukraine of returning 22 howitzers to the frontline, but Ukraine's Lysenko said government troops had completed the process of withdrawing tanks, artillery and mortars as required by the peace agreement.
Under the cease-fire deal, both sides are meant to have withdrawn most weapons from the frontline as part of a 12-point peace plan designed to end a conflict that has killed over 8,000 people since April 2014.