Ukrainian President Petro Poroshenko will cut short his visit to an economic forum in Davos, Switzerland, to head home in view of the "worsening situation" in rebel-held eastern Ukraine, his spokesman said.
"The armed forces chief of staff and the defence minister have just reported to him on the situation near the Donetsk airport," Sviatoslav Tsegolko said on Facebook.
"In view of the worsening situation, the president has decided to cut short his visit to Switzerland and will return to Ukraine tomorrow."
Ukraine earlier accused Russian forces of attacking its soldiers fighting pro-Kremlin insurgents in the ex-Soviet republic's separatist east.
"In violation of all prior agreements, Ukrainian military units were attacked in the north (of the war zone) by regular units of the Russian armed forces," Ukrainian military spokesman Andriy Lysenko told a hastily convened press conference in Kiev.
The charge came only hours after Moscow denied claims by Kiev of about 700 new Russian soldiers crossing over into eastern Ukraine to help the rebels' latest advance on government troops.
It also marked the first time that Kiev has accused Russian soldiers of attacking its forces since the warring sides signed an often-violated 5 September truce.
Mr Lysenko said the attack happened in the separatist Lugansk province - the region the Russian forces had allegedly entered the day before.
The claims are likely to add to tensions surrounding high-stakes talks in Berlin tomorrow aimed at stemming the latest spike in violence in a conflict that has claimed more than 4,800 lives.
