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At least four people have been killed and 19 injured after a passenger bus hit a landmine in eastern Ukraine, local officials say.

They say the accident happened as the vehicle tried to bypass a checkpoint near Artemivsk, the government-held town in the Donetsk region.

The bus was travelling from Artemivsk to the city of Horlivka, which is being held by pro-Russian rebels.

The rebels seized large parts of the Donetsk and Luhansk regions in April.

"Initial reports say the driver took the decision to bypass the checkpoint and move on a dirt road," said Vyacheslav Abroskin, the regional head of Ukraine's interior ministry.

"As he was driving through the field, the rear wheel ran over a mine," he added.

Horlivka lies north of Donetsk, the main rebel stronghold.

The regions is littered with landmines, following months of fierce fighting between Ukrainian government troops and the separatist that left more than 6,000 people dead.

A ceasefire agreed in February is largely holding, although both sides accuse each other of sporadic shelling.

The Kiev government, Western leaders and Nato say there is clear evidence that Russia has helped the rebels with troops and heavy weapons.

Russia denies that, insisting that any Russians on the rebel side are "volunteers".

Last March, Russia annexed Ukraine's southern Crimea peninsula - a move widely condemned around the world.