Pro-Russian rebels in Donetsk have said they plan to stay on the attack against Kiev’s forces, as the Russian president Vladimir Putin blamed “criminal orders” from the Ukrainian government for increased violence in the east of the country.

“There will be no more ceasefires,” said rebel leader Alexander Zakharchenko at a meeting with students, a day after an attack on a trolleybus in Donetsk left up to 13 dead. Zakharchenko said Ukraine was currently mobilising recruits and had been planning a new assault.

“We took the decision not to wait for the Ukrainian army to attack. We will attack them until we have reached the borders of the former Donetsk region,” said Zakharchenko, indicating an area that includes a number of towns currently under Ukrainian control, including the port city of Mariupol.

The UN human rights office says the conflict in eastern Ukraine has now left 5,000 people dead, including 262 in the past nine days alone.

A ceasefire was agreed at talks in Minsk in September but has never really held. The Russian and Ukrainian foreign ministers met on Wednesday evening in Berlin and again affirmed the document, calling on heavy artillery to be withdrawn from the front lines, but the situation on the ground has only got worse.

Already this week the rebels have regained control over the remains of Donetsk airport, which has been controlled by the Ukrainians since the start of the conflict, and appear to be moving in on the town of Debaltseve, where Ukrainian troops are under siege.

In televised comments, Putin blamed the renewed violence on Ukrainian forces: “The Kiev authorities have given an official order to start large-scale military operations practically throughout the whole line of contact. The result is dozens of killed and wounded, not only among the military on both sides but... among civilians,” Putin told senior state officials.

At the World Economic Forum in Davos, Switzerland, Russia’s deputy prime minister, Igor Shuvalov, said: “The west does not treat Russia as an equal partner, and this will make the conflict in Ukraine a bleeding wound for decades.” He blamed the west also for sanctions against Russia, which have combined with falling oil prices to deal a hefty blow to the rouble in recent months. German’s chancellor Angela Merkel said this week that the sanctions should not be lifted yet.

The Ukrainian president, Petro Poroshenko, said this week there were 9,000 regular Russian troops in Ukraine. Russia has denied that there are any, and denies even supplying military hardware to the rebels, despite the obvious evidence of such transfers on the ground.

The military rhetoric on both sides has intensified in recent days, with Poroshenko taking to Twitter on Thursday evening to say that if the rebels did not abide by the ceasefire, Kiev’s supporters would “give it to them in the teeth”.

Much remains unclear about the bus attack in Donetsk on Thursday. Rather like an attack on a Ukrainian checkpoint this month that also left 13 dead, both sides have blamed the other. In the earlier incident, international monitors said it appeared that the bus had been hit by missiles fired by rebels.

This time, Ukraine’s prime minister, Arseniy Yatsenyuk, said the attack had been carried out by “Russian terrorists”, while rebels said a Ukrainian “diversionary group” operating behind rebel lines was responsible for carrying out the attack. However, no further information about the group, which rebels said they had detained, has been forthcoming.