Pro-Russian separatists reportedly broke their cease-fire agreement with the Ukrainian government by shooting down a military helicopter on Tuesday afternoon, killing all nine people on board, a military spokesman said.

Rebels shot down a Ukrainian military MI-8 helicopter on the outskirts of Slovyansk, which has been gripped by violence in the past couple of months and is now being held by rebels, the New York Times reported.

The helicopter was transporting goods and equipment to monitor the cease-fire, Vladislav Seleznyov, a spokesman for the Ukrainian government, said in a statement posted online.  Preliminary results show the helicopter was most likely shot down by a shoulder-launched missile, though the Times reported that rebels have yet to take responsibility for the attack.

This missile attack comes hours after Russian President Vladimir Putin announced a request to extend the cease-fire past June 27 and urged Ukraine's newly elected President Petro Poroshenko to talk to the rebels, Reuters reported.

Poroshenko has insisted that he won't speak to rebels who have “blood on their hands.”