Ukraine on Sunday suspended operations at one of the seven checkpoints to territory in the eastern Donbass region controlled by Russia-backed separatists, due to heavy shelling, the Ukrainian military said.

Incidents of shelling across the line dividing government forces and separatists increased sharply last week, in what the Ukrainian government called a provocation. Kyiv's Western allies say Russia is preparing to invade Ukraine and are concerned that the escalation might be used as a pretext.

Russia denies any plans to attack its neighbour, while Ukraine strongly denied suggestions by Moscow that Kyiv could launch an offensive in eastern Ukraine.

Separatists on Saturday fired three times on the Schastya checkpoint using mortars and heavy anti-tank grenade launchers, as ceasefire violations by separatists along the frontline increased to 136 from 66 on Friday, the military said on its Facebook page.

Two Ukrainian soldiers were reported killed and four wounded on Saturday.

Considering "the escalation of the situation... and the inability to guarantee the safety of the civilian population" using the checkpoint, the command was suspending its use from 8 a.m. (0600 GMT) on Sunday "for the period of the threat," the military said.

Separatist officials accused Ukraine on social media site Telegram of shelling separatist-controlled areas and said they had to respond accordingly.

(Reporting by Natalia Zinets; Editing by William Mallard)