A Kiev offensive to retake control of restive areas along the country's eastern border has accelerated in recent days, prompting leaders of an armed pro-Russia uprising to appeal to Moscow for urgent military help on Tuesday.

Ukrainian government troops have advanced from the north and south in a bid to cut off the fighters and weapons that Kiev says are flowing over its border from Russia. So far, though, Moscow has given little sign it intends to respond to repeated requests from separatists and send in troops to assert...