President Vladimir Putin on Thursday warned Kiev of "very serious consequences for Ukrainian statehood" if it were to launch military action against pro-Russian rebels in the east during the football World Cup, which begins in Russia next week.
Zakhar Prilepin, a Russian writer who advises rebels in the Russian-backed, separatist Donetsk region, asked Putin during a televised phone-in to comment about the possibility of Ukraine launching military action during the month-long tournament.
"I hope that there won't be any provocations but, if it happens, I think it would have very serious consequences for Ukrainian statehood in general," Putin said.
Russia is hosting the World Cup from June 14 to July 15 in 11 Russian cities including Rostov-on-Don, some 100 km (60 miles) from the border with Ukraine.
More than 10,000 people have been killed since April 2014 in a conflict that pits Ukrainian forces against Russian-backed separatists in eastern Ukraine.
Intermittent clashes persist despite a notional ceasefire and diplomatic peace efforts.