Armed men shot down a Ukrainian helicopter carrying technicians who had been installing equipment to monitor violations of a peace plan in Ukraine's rebellious east on Tuesday, June 24, killing all nine people on board, a military spokesman said, according to Reuters.

The technicians had been returning from setting up specialised equipment when their Mi-8 cargo helicopter was struck by a missile near Slaviansk in eastern Ukraine, government forces spokesman Vladyslav Seleznyov said.

"There were 9 people on board. According to preliminary information ... all those on board were killed," Seleznyov said on his Facebook page. The nine dead included a three-man crew.

"The (rebel) fighters, having fired the rocket, hid in the nearby village of Bylbasovka," he said.

The incident took place just hours after pro-Russian armed men on Monday night announced a ceasefire until June 27 to match a week-long truce by government forces which has been ordered by President Petro Poroshenko.

It was the second time a helicopter has been brought down by rebel fire from Slaviansk. On May 30, a military helicopter was downedkilling 14 servicemen, including one general.