The bus riddled with bullet holes at a checkpoint of the Ukrainian forces in the village of Bugas, south of Donetsk, yesterday. Photo: Ukraine's Ministry of Internal Affairs/Handout via Reuters

A passenger bus came under heavy fire in eastern Ukraine yesterday, killing at least 10 people, Ukrainian authorities said, and fighting intensified around the international airport in the city of Donetsk as separatists tried to oust government forces.

The latest violence flared after Russia, Ukraine, France and Germany scrapped plans for a summit in Kazakhstan this week because of the failure to implement a four-month-old ceasefire agreement.

A senior official from the Organisation for Security and Cooperation in Europe (OSCE) called for maximum restraint from all sides in the Ukraine conflict, which has killed more than 4,700 people since last April.

“Over the past 24 hours the situation has significantly deteriorated, especially near the Donetsk airport. More civilian casualties have been reported elsewhere,” said Ertugrul Apakan, head of the OSCE special monitoring mission in Ukraine.

The war between Ukrainian forces and pro-Russian rebels broke out soon after Russia annexed Crimea last year, creating the worst crisis in East-West relations since the Cold War. Western governments accuse Russia of backing the separatists, including by sending in troops, which it denies.

Photographs showed the bus peppered by holes, as were seats inside it. A long trail of blood marked the road beside it near the town of Volnovakha.

“Ten people have been killed and at least 13 are wounded,” a regional Ukrainian administration spokesman said. He said the bus was attacked by rebels using Grad rocket launchers while it was carrying civilians through a government checkpoint.

Separatists denied responsibility and said the bus had been attacked by small arms fire rather than a missile or shell.

Reports from Donetsk said a significant part of the airport’s multi-storey control tower – already a wrecked hulk with cabling and concrete dangling from it after months of shelling – had been destroyed.

The Sergei Prokofiev airport complex, opened to great fanfare by the now ousted president Viktor Yanukovych to mark the Euro 2012 soccer championship, has progressively disintegrated under months of fire.

After a night of attacks from separatists using Grad missile launchers, the rebels began firing from tanks on the airport’s new terminal, which was still being held by Ukrainian government forces, the Kiev military said in a statement.

“The Russian military and the terrorists have deliberately chosen the tactic of escalation of tension,” military spokesman Andriy Lysenko told journalists. One Ukrainian soldier had been killed and 10 wounded in overnight fighting.

Although it has not functioned since the onset of hostilities last April, with its runways cratered by shell holes, the airport has symbolic value for both sides. Government forces have repelled repeated rebel attempts to dislodge them.