Russian-backed rebels and Ukrainian forces traded accusations on Thursday that each had fired across the ceasefire line in eastern Ukraine, raising alarm at a time when Western countries have warned of the possibility of a Russian invasion any day, Reuters reported.

The details of the incidents could not be independently confirmed, and the initial reports suggested they were on a similar scale to ceasefire violations that have been common throughout the eight year conflict.

But they come at a time of global concern over the prospect of a wider war, with more than 100,000 Russian troops near the Ukrainian frontier. Moscow denies it is planning an invasion and has said this week it is pulling back some troops, though Western countries say they are not convinced.

The separatists accused government forces of opening fire on their territory four times in the past 24 hours, while Ukraine accused the rebels of firing shells, including some that struck a kindergarten, causing shell-shock to two civilians.

A Reuters photographer in the town of Kadiivka in Ukraine's rebel-held Luhansk region heard the sound of some artillery fire from the direction of the line of contact but was not immediately able to assess the details of the incident.

Kyiv and its Western allies have repeatedly said in recent weeks that they believe Moscow could use an incident in the separatist conflict as justification for an invasion. Russia, for its part, has accused Kyiv of trying to provoke an escalation to recapture rebel territory by force.

A diplomatic source said a longstanding monitoring mission from the Organization for Security and Cooperation in Europe had recorded multiple shelling incidents along the line of contact in the early hours of Thursday.

Since a 2015 ceasefire brought an end to major combat in the separatist conflict, the OSCE has typically reported dozens of ceasefire violations each day, with significant shelling or clashes leading to injuries or death several times a month.

The self-proclaimed Luhansk People's Republic, one of two rebel regions, said Ukrainian forces had used mortars, grenade launchers and a machine gun in four separate incidents on Thursday.

"Armed forces of Ukraine have crudely violated the ceasefire regime, using heavy weapons, which, according to the Minsk agreements, should be withdrawn," the separatists said in a statement.

Referring to the rebels, Ukraine's military said: "With particular cynicism, the Russian occupation troops shelled the village of Stanytsa Lugansk in the Luhansk region. As a result of the use of heavy artillery weapons by terrorists, shells hit the kindergarten building. According to preliminary data, two civilians received shell shock."

Russia's lower house of parliament voted on Tuesday to ask President Vladimir Putin to recognise the two self-proclaimed separatist republics as independent.

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