DONETSK (AFP) ― NATO on Wednesday accused Russia of sending tanks, troops and military hardware to east Ukraine, raising fears of renewed all-out fighting and calling into question the Minsk peace deal.

Moscow denied the claims as “unfounded” and the deputy ambassador to the United Nations, Alexander Pankin, told an emergency Security Council meeting that the alliance was making “another foray into propaganda.”

The United States warned it was ready to work with allies in Europe to slap more sanctions on Russia for supporting pro-Moscow separatists in east Ukraine, who have been battling Kiev since April.

“We have seen columns of Russian equipment, primarily Russian tanks, Russian artillery, Russian air defense systems and Russian combat troops entering into Ukraine,” U.S. Gen. Philip Breedlove, NATO’s commander in Europe, said in Sofia.

“We do not have a good picture at this time of how many. We agree that there are multiple columns that we have seen,” he added.

The claims come amid growing fears of a return to all-out conflict despite a two-month ceasefire which has stopped much frontline fighting but not shelling at strategic flashpoints.

“We are deeply concerned by the possibility of a return to full-scale fighting,” U.N. Assistant Secretary-General Jens Anders Toyberg-Frandzen told the Security Council.

Ukraine’s Defense Minister Stepan Poltorak said Kiev was preparing for a possible new round of fighting after seeing “increased activity” by Russia and pro-Moscow rebels in the east.

“The main task I see is to prepare for combat operations. We are doing this, we are readying our reserves,” Poltorak said at the start of a cabinet meeting in Kiev.

Observers from the Organization for Security and Cooperation in Europe reported seeing a convoy of 43 unmarked military trucks ― five towing Howitzer heavy artillery pieces and another five towing multilaunch rocket systems ―travelling into the rebel stronghold of Donetsk on Tuesday.