Russian President Vladimir Putin speaks in Moscow
Vladimir Putin accused Kiev of making criminal ordersReuters

Russian President Vladimir Putin has blamed Kiev for an escalation in violence in eastern Ukraine as pro-Russian separatists ruled out fresh peace talks with the government.

Putin's remarks amount to a hardening of Russia's position on the conflict, which has already led to the death of more than 5,000 people, according to the United Nations human rights office. The office said the conflict was now in its "most deadly period," since a ceasefire was agreed in September 2014.

"The Kiev authorities have given an official order to start large-scale military operations practically throughout the whole line of contact. The result is tens of killed and wounded, not only among the military on both sides but... among civilians," Putin said in a televised statement. "Those who give criminal orders are responsible."

The two sides had previously agreed to a ceasefire in the Belarusian capital of Minsk last September, brokered by the European Union.

The deal has come under strain in recent weeks, with deadly skirmishes leading to hundreds of deaths in eastern Ukraine.

Putin condemned Ukraine's President Petro Poroshenko for ignoring the Kremlin's proposal to withdraw heavy weaponry from the de-facto border between Ukraine and the self-declared rogue republics, established by the separatists.

Ukraine said earlier this week that Russia had 9,000 troops on its territory and it urged the Kremlin to withdraw its forces.

For its part, Moscow has denied sending troops over its border to support the separatist rebels.

Meanwhile, the head of the self-proclaimed Donetsk People's Republic said the group would not seek to compromise with Kiev.

"There will be no attempts to speak about a ceasefire on our part," said rebel leader Alexander Zakharchenko, as cited by Interfax news agency. "If Poroshenko comes here, we will talk. We are advancing now, [so,] what talks?"

The rebels recently defeated government forces and took control of the main terminal of Donetsk airport, in a significant military victory for the group.