An Ukrainian officer examines an automatic grenade launcher during a presentation of new military equipment near Goncharivsk. Pro-Russian rebels vowed Jan. 23 to conquer more territory in eastern Ukraine. (Sergei Supinsky/AFP/Getty Images)

Pro-Russian separatists in Donetsk rejected an existing cease-fire arrangement Friday, saying they would not initiate further peace talks, as their leader announced plans to expand rebel territory — moves that all but guarantee fresh confrontations in eastern Ukraine.

Alexander Zakharchenko, head of the self-declared Donetsk People’s Republic, said that the rebels were regaining ground from Ukrainian government forces and will not stop until they control the entire Donetsk region.

He also warned Ukrainian security forces that rebels will no longer take prisoners, meaning that troops in their way now face a fight-or-die scenario.

Pro-Russian rebels in Donetsk and Luhansk have theoretically been under a cease-fire with Ukrainian forces since September. But the agreement was always tenuous, and recent clashes had pushed it to the brink of collapse. Zakharchenko’s deputy, Eduard Basurin, was quoted by the separatist-run Donetsk News Agency on Friday as saying that separatists no longer recognized the agreement signed in Minsk, Belarus — although, he added, the rebels were open to negotiations.

But Zakharchenko made it clear that to get rebels back to the table, Kiev would have to make a bold first step — such as sending Ukrainian President Petro Poroshenko to negotiate. “There will be no more attempts to speak about a cease-fire on our part,” Zakharchenko told a group of university students Friday.

Several people were killed in an attack on a bus Thursday morning in the rebel-controlled city of Donetsk in eastern Ukraine. Windows of shops nearby were blown out by the blast. (Reuters)

Rebel forces opposed to Kiev’s Western-leaning policies were emboldened after the partial withdrawal of Ukrainian military units on Thursday from the Donetsk airport, a key battleground.

A Ukrainian military spokesman said Friday that Kiev’s forces will observe the lines set by the Minsk cease-fire accords, despite claims that rebels have carried out steady attacks.

But Kiev has not shown any sign that it intends to back down if fired on.

“We will fight back,” Poroshenko said during a meeting with security officials Thursday.

Zakharchenko said rebels would fight the Ukrainian military “to the borders of the Donetsk region,” citing current gains.

Military officials in Kiev expressed skepticism about his claims, arguing that the rebels had gained no territory beyond that around Checkpoint 31 in the Luhansk region.

“To speak about how realistic these messages are, it’s very difficult,” Col. Andriy Lysenko, a spokesman for the Ukrainian National Security and Defense Council, told reporters on Friday. “Those statements, that they will stop the peace? There has never been a day when they didn’t shell. They shelled less on some days, but it never stopped.”

A Russian backed separatist rebel takes cover from shelling in the Kievsky district of Donetsk, Ukraine, on Jan. 22. (Manu Brabo/AP)

But earlier this week, Ukrainian and Western leaders were worried that rebels were making “a very blatant land grab,” as U.S. Secretary of State John F. Kerry put it Wednesday.

The United Nations raised its estimate of deaths in the Ukraine conflict Friday to almost 5,100 since fighting began in April — 262 in the past nine days, making it the deadliest period since the Minsk cease-fire agreement was struck.

Ukraine maintains that the surge in hostilities is the result of Russian reinforcements crossing the border into eastern Ukraine. Lysenko claimed that more than 9,000 Russian troops are in Ukraine, “the highest number since the beginning of the conflict,” he said.

Russia has denied such accusations, even as international leaders have buttressed the charges.

On Thursday, NATO’s top commander, U.S. Air Force Gen. Philip M. Breedlove, said the alliance had detected air and weapons systems “that have accompanied past Russian troop movements into Ukraine.”

Russian President Vladimir Putin, however, blamed Kiev on Friday. He complained that Ukrainian officials ignored a Kremlin-drafted peace proposal last week, instead issuing “an official order to start large-scale fighting along practically the entire perimeter of contact between the opposing sides.”

Putin’s peace proposal, sent to Poroshenko on Jan. 15, suggested a cease-fire and a demarcation line from which both sides could withdraw their largest weapons.

At the United Nations, U.S. Ambassador Samantha Power called the proposal “a Russian occupation plan” on Wednesday.

Tensions between Russia and the West remain high, despite recent overtures from NATO officials to meet with Russian leaders, as European leaders decided this week against rolling back Russian sanctions over developments in Ukraine.

At the World Economic Forum in Davos on Friday, Russian First Deputy Prime Minister Igor Shuvalov warned the West against trying to push Putin through sanctions.

“If a Russian feels any pressure from outside, he will never, never turn away and give up his leader,” Shuvalov said, adding that Russians would eat less and use less energy before they would abandon Putin, and that if sanctions continue, “it will be a bleeding wound for decades.”