KIEV/DONETSK - Pro-Russian separatists shot down a Ukrainian warplane in eastern Ukraine overnight into Sunday while at least 10 civilians were killed in fighting involving artillery and mortar in the rebel-held city of Donetsk, local authorities said.
The renewed fighting, which followed a claim by rebels that they were receiving fresh stocks of heavy military equipment from Russia and 1,200 fighters, cast a shadow over a high-level international meeting in Berlin involving Russia and Ukraine.
The four-month conflict in Ukraine's Russian-speaking east has reached a critical phase, with Kiev and Western governments watching nervously to see if Russia will intervene in support of the increasingly besieged rebels - something denied by Moscow.
A Ukrainian military spokesman said the rebels had hit a MiG-29 fighter jet over the Luhansk region, one of two regions where entrenched separatists are fighting a rear-guard action to hold off government forces advancing on their positions.
The pilot ejected and was located and recovered after a search, the spokesman, Oleksiy Dmytrashkivsky, told Reuters.
Donetsk, the region's biggest city where rebels are also still dug in despite an encroaching government offensive, rocked to the crash and boom of heavy weapons in the south throughout the night.
At least 10 civilians have been killed, local authorities said.
The Ukrainian National Guard said its forces had seized a rebel field commander from Luhansk region as well as 13 others suspected of "terrorist activity".
"The terrorists are putting on ordinary clothes, taking only their passport with them and are trying to pass themselves off as ordinary peaceful citizens on public transport to try to get through the Ukrainian checkpoints," it said. "Among those seized is a field commander of the Luhansk terrorist group."
On Saturday, Alexander Zakharchenko, prime minister of the self-proclaimed Donetsk People's Republic, said rebels were in the process of receiving some 150 armoured vehicles, including 30 tanks, and 1,200 trained fighters with which they planned to launch a major counter-offensive against government forces. "They are joining at the most crucial moment," he said in a video recorded on Friday. He did not specify where the vehicles would come from.
The renewed fighting and rebel claims of reinforcements from Russia was certain to be broached at a meeting scheduled in Berlin later on Sunday of Ukrainian, Russian, German and French foreign ministers.
France said the meeting could be a first step towards a peace summit.
Moscow has come under heavy Western sanctions over its annexation of Ukraine's Crimea and accusations it is supporting the separatists with fighters, arms and funds. Russia denies those charges.