“The Russian military has deployed a large amount of artillery and multiple rocket launcher systems around Debaltseve where it is shelling Ukrainian positions,” State Department spokeswoman Jen Psaki told reporters. “We are confident that these are Russian military, not separatist systems.”

Psaki added that the Russian military also has air defense systems deployed near the town, which is a key point for coal supply.

“Russian units along the border with Ukraine are preparing a large shipment of supplies to pro-Russian forces fighting in eastern Ukraine. This is clearly not in the spirit of this week’s agreement,” Psaki said.

A cease-fire agreement for Ukraine was brokered in Minsk after 17 hours of negotiations Thursday. It set a halt to hostilities for midnight Saturday. 

The talks for a settlement of the conflict in the Donbass region of Ukraine included Russian President Vladimir Putin, Ukrainian President Petro Poroshenko, German Chancellor Angela Merkel and French President Francois Hollande, as well as participants of the OSCE’s Trilateral Contact Group, which included representatives of the separatist territories.

But in the interim, rebel pro-Russian separatists launched a major offensive to capture the economic hub of Debaltseve on Friday.

At least eight Ukrainian soldiers were killed and another 34 wounded during clashes with pro-Russian separatists in eastern Ukraine, according to Ukraine’s Counterterrorism Center.

Psaki called for the release of Nadiya Savchenko, a Ukrainian pilot who has been in Russian custody, and charged with the deaths of two Russian journalists in eastern Ukraine.  

“She’s a hostage of the Russian government, and she must be released immediately,” she said. “This week’s agreement calls for the exchange of all hostages and a illegally-held persons taken during the conflict.”