Arseniy Yatsenyuk
Ukraine Prime Minister Arseniy Yatsenyuk addresses the UN General AssemblyReuters

Ukrainian Prime Minister Arseniy Yatsenyuk has warned of a war with Russia if Kiev cannot bring Moscow's involvement in the country's east to a halt.

His comments came before a vote that saw him supported by Ukrainian lawmakers to remain the prime minister of Ukraine, with 341 politicians backing him out of the 450-seat legislature.

"Our country is at war. People are in trouble," Yatsenyuk told legislators. "It depends on us whether we can stop the external aggression from Russia."

"Now there is a proposal to form the cabinet quickly," he said. "2015 will be more difficult than 2014. Let's start working."

After the vote to keep Yatsenyuk as prime minister, Parliamentary Speaker Volodymyr Groysman announced the Ukrainian parliament would approve his cabinet on 2 December.

Elsewhere, Ukrainian President Petro Poroshenko announced his plans to prepare the country's defence against the military threat emanating from its restive eastern regions.

He said there was little choice but to "militarise society to some extent", increasing defence expenditure, maintaining conscription and reintroducing army training in the country's schools.

"We will sometimes have to even sleep with a gun under the pillow. The enemy is on our doorstep," he told parliament after it opened.

In another measure that threatened to worsen relations with Russian-speaking separatists in the country's east, Poroshenko revealed Ukrainian would become Ukraine's sole official language.