Ukraine's Prime Minister Arseniy Yatsenyuk has called on the West not to lift sanctions against Russia until the government regains full control of its territory.

Speaking at the United Nations General Assembly, Yatsenyuk said his government was still battling Russian troops in eastern Ukraine.

Moscow has denied it has any soldiers operating in its neighbour's territory and has always denied Western accusations it is arming the separatist rebels.

Moscow annexed the Crimea peninsula in March, after a referendum condemned as illegal by the United States and the European Union.

In response, the US and EU have imposed sanctions on Russian individuals, companies and broader sectors of the economy.

The Western sanctions were accompanied with stern warnings to the Kremlin that it should move to de-escalate the crisis in Ukraine. Yet, the violence has continued in Ukraine's east, where the UN estimates that 3.245 people have been killed since violence erupted in mid-April.

A ceasefire has largely held in the east of the country, although sporadic outbreaks of violence have led to more deaths in recent weeks.

"We ask our partners not to lift sanctions until Ukraine takes control of its entire territory," Yatsenyuk told the UN General Assembly in New York.

"Russian troops are deployed in the east of Ukraine," he said. "We urge Russia to pull back its forces... and to start real talks."

"Every day, despite the ceasefire, we are losing Ukrainian soldiers, we are losing civilians," he said.

Nato said on September 24 it witnessed a large withdrawal of Russian troops from the east of Ukraine, although it stressed that some troops remained in Ukrainian territory.

Meanwhile, US President Barack Obama offered Russia a way out of the geopolitical standoff, if it made sincere efforts to de-escalate the crisis in Ukraine.

Obama criticised Russia's actions to date but said if Russia took a peaceful path, "then we will lift our sanctions and welcome Russia's role in addressing common challenges."