A military helicopter was shot down in eastern Ukraine by pro-Russian rebels on Thursday, killing 14 people, marking an increase in violence since incoming President Petro Poroshenko was elected earlier this week.

"I have just received information that terrorists using Russian anti-aircraft missiles shot down our helicopter near Slovyansk. It had been ferrying servicemen for a change of duty," said outgoing President Olexander Turchynov, according to Reuters. A general was among the 14 people on board the helicopter who were killed.

Turchynov said the helicopter was shot down after it dropped off troops at a military base, the BBC reported.

Poroshenko said he was committed to crushing the uprising in eastern Ukraine, where separatists aligned with Russia are attempting to break away from Ukraine. He called the rebels “bandits” and “murderers,” according to the BBC.

Meanwhile, four international monitors from the Organization for Security and Cooperation, or OSCE, in Europe being held in eastern Ukraine by insurgents will soon be released, the city’s self-proclaimed mayor told Associated Press, or AP.

"I addressed the OSCE mission to warn them that their people should not over the coming week travel in areas under our control. And they decided to show up anyway," Slovyansk “People’s Mayor” Vyacheslav Ponomarev told AP. “We will deal with this and then release them.”