By Michael Hernandez

WASHINGTON

 Secretary of State John Kerry on Thursday singled out Russian-backed rebels for what he said is a “very blatant land-grab” in eastern Ukraine.

Rebels have attacked the town of Debaltseve, some 45 miles (70 kilometers) northeast of the rebel-held city of Donetsk.

Kerry said the offensive was “an attempt to obviously gain control of a very significant rail juncture,” and to expand their territorial control in the country despite a September cease-fire deal.

The U.S.'s top diplomat said there has been a roughly 500-square-mile (805-square-kilometer) extension past the line of control agreed to in September.

"This is a very blatant land grab and it is in direct contravention to the Minsk agreements which they signed up to," Kerry told reporters during a joint press conference with EU High Representative Federica Mogherini at the State Department. 

The Ukrainian government and pro-Russian separatists signed the agreement Sept 5 in Minsk, but both sides have violated its terms.

The EU and U.S. have imposed coordinated waves of sanctions against Russia for what they say are Russia’s destabilizing actions in the country, including support for rebels who have attempted to carve out autonomous regions in Ukraine.

The EU is set to review its set of sanctions in March, with Mogherini saying that the decision “is going to be based only on the full implementation of the Minsk agreement.”

At least 1,363 fatalities have been recorded since the cease-fire.