Ukraine has begun an “anti-terrorist operation” in the east of the country, it’s been reported.

Ukrainian troops disembarked at least two helicopters at an airfield on the outskirts of the eastern city of Kramatorsk, witnesses told news agency Reuters.

Local journalists quoted by Interfax said automatic firing could be heard from the direction of Kramatorsk’s military airfield and said a fighter jet had swooped low over the area.

A correspondent of Espresso TV meanwhile said the Ukrainian plane had been trying to land but had not been able to do so because separatists had opened fire on it.

Earlier, in Parliament, the interim president Olexsandr Turchynov said the operation would happen in carefully-planned stages, step by step.

“This morning an anti-terrorist operation has started in the east of the Donetsk region,” he said. “The aim of this action – I emphasise it once again – is to protect Ukraine’s citizens, to stop terror, to stop criminality, and stop attempts to tear Ukraine apart.”

Turchynov spoke 24 hours after an ultimatum expired for the separatists to lay down their arms.

Eastern towns were described as quiet on Tuesday morning – with no repetition of Monday’s scenes when rebels took over a police station at Horlivka.

But the situation remains tense. Western governments fear a repeat of events in Crimea, which Russian troops seized in February.