DONETSK, Ukraine — Signs emerged Friday of a major rebel offensive looming in eastern Ukraine, which has seen a surge in fighting and deadly attacks despite diplomatic efforts to craft a lasting peace deal.
One separatist leader said his pro-Russian rebels have launched a multi-pronged offensive and won't join further peace talks — but left unclear whether they would respect this week's agreement to pull back heavy weapons from the front line.
A top NATO official said the Russian-backed rebels in eastern Ukraine have been beefed up and have pushed further west. U.S. Air Force Gen. Philip Breedlove said air defense and electronic warfare equipment have been detected in the area that, in the past, coincided with the incursion of Russian troops into Ukraine.
Russia insists that it does not support the rebels, but Western military officials say the sheer number of heavy weapons under rebel control belies that claim.
The U.N. human rights agency, meanwhile, raised its estimate Friday of the conflict's overall death toll to nearly 5,100 since April due to the escalation of fighting.
A pro-Russian insurgency flared up in April in the Donetsk and Luhansk regions in eastern Ukraine following Russia's annexation of Ukraine's Crimean Peninsula, and in May they declared independence from the central government in Kiev.
Separatist leader Alexander Zakharchenko said rebel fighters will fight for more territory and were advancing in several directions to push Ukrainian forces back to the edge of the Donetsk region. Donetsk, the largest rebel-held city, was hit this week with mortar attacks and fighting over its war-wrecked airport that killed at least 30 people.
"Attempts to talk about a cease-fire will no longer be undertaken by our side," Zakharchenko said.
Any rebel advances would further undermine a tentative peace deal forged this week in Berlin at a meeting of foreign ministers from Russia, Ukraine, France and Germany. Those negotiations concluded with an agreement to uphold a demarcation line defined in September.
The plan calls for Ukrainian troops and Russian-backed separatists to pull back their heavy arms 15 kilometers (9 miles) on either side of the line, although there was no agreement on a withdrawal of troops.
Battles intensified last weekend over Donetsk airport, a gleaming showcase for the Euro 2012 soccer championship that has been reduced to piles of rubble and steel beams by months of clashes. Rebels eventually took control of its terminal, although fighting is still going on in nearby areas.
At the international economic forum in Davos, Switzerland, a Russian deputy prime minister vowed that Moscow would not be cowed by the sanctions the West has imposed upon Russia for its actions in Ukraine.
Igor Shuvalov warned the West against trying to topple Russian President Vladimir Putin, reflecting the Kremlin's view that the European Union and U.S. sanctions are aimed at regime change.
"When a Russian feels any foreign pressure, he will never give up his leader," Shuvalov said Friday. "We will survive any hardship in the country — east less food, use less electricity."
The Russian currency has lost half its value in recent months from the double blow of sanctions and a plunge in world oil prices.
Ukrainian President Petro Poroshenko appeared to still be holding out hope for a new cease-fire, but said stern retribution would await anybody violating the peace. After a speech Wednesday at Davos, he rushed home to deal with the escalating fighting.
"If the enemy doesn't want to abide by the cease-fire, if he doesn't want to put an end to the suffering of peaceful people, Ukrainian villages and town, we will smash them in the teeth," Poroshenko told top defense officials.