(Reuters) - Fighting flared in the eastern Ukrainian city of Donetsk on Monday as investigators began to inspect the bodies of victims of the downing of Malaysia Airlines flight MH17 last week.

The fighting in Donetsk served as a reminder of the dangers the experts face working in a war zone. International inspectors got access to the remains of hundreds of victims stored in refrigerated railway wagons near the crash site but governments expressed concern over broader access to the rebel-held area.

The government in Kiev denied sending the regular army into the center of Donetsk, which pro-Russian separatists captured in April, but said small "self-organized" pro-Ukrainian groups were fighting the rebels in the city.

Four people were killed in clashes, health officials said.

Artillery fire sent plumes of smoke skywards in Donetsk, around 60 km (40 miles) from the crash site, in what the separatists said was an attempt by government forces to enter the city they seized in April. The clashes quickly subsided.

Donetsk is at the heart of a rebel uprising against rule by Kiev, and Ukrainian President Petro Poroshenko has vowed to retake the city as part of what Kiev calls its "anti-terrorist operation" against the separatists.

DISASTER VICTIMS

Against a background of international horror over the fate of the remains of the 298 victims of the Malaysia Airlines disaster, the first international investigators reached eastern Ukraine on Monday.

Three members of a Dutch disaster victims identification team arrived at a railway station near the crash site where rebels say 247 bodies have been stored in refrigerated wagons. About two thirds of the crash victims were Dutch.

The head of the team inspected the storage of the bodies in the rail cars and, despite an overwhelming stench of decomposition when the doors were opened, said it was fine.

"The storage of the bodies is of good quality," said Peter van Vliet, whose team went through the wagons dressed in surgical masks and rubber gloves.

Van Vliet said he had been told the train would be leaving the station at Torez later on Monday so that bodies can be taken to where they can be identified and repatriated. He could not say where it was going.

Ukrainian officials said as of Monday morning 272 bodies and 66 fragments of bodies had been found.

The shooting down of the airliner on Thursday has sharply deepened the Ukrainian crisis, in which separatists in the Russian-speaking east have been fighting government forces since protesters in Kiev forced out a pro-Moscow president and Russia annexed Crimea in March.

The United States and its allies have blamed the pro-Russian rebels for downing of the plane.

Russia's defense ministry challenged accusations that pro-Russian separatists were responsible for shooting down the airliner and said Ukrainian warplanes had flown close to it.

The ministry also rejected accusations that Russia had supplied the rebels with SA-11 Buk anti-aircraft missile systems - the weapon said by Kiev and the West to have downed the airliner - "or any other weapons".

SHOCK TURNS TO ANGER

U.S. Secretary of State John Kerry laid out what he called overwhelming evidence of Russian complicity in the shooting down of the Malaysia Airlines plane, and expressed disgust at how the bodies of the victims had been treated at the crash site.

"Drunken separatists have been piling bodies into trucks and removing them from the site," he said on NBC television on Sunday. "What's happening is really grotesque and it is contrary to everything President Putin and Russia said they would do."

Television images of the rebel-controlled crash site, where the remains of victims had lain decomposing in fields among their personal belongings, have turned initial shock and sorrow after Thursday's disaster into anger.

Australian Prime Minister Tony Abbott said he had spoken to Putin for the first time about the disaster. At least 27 Australians were on the flight from Amsterdam to Kuala Lumpur.

Abbott said an Australian investigation team was in Kiev but had been unable to travel to the site. He said there had been some improvement with the Ukrainian government offering access.

"But there's still a hell of a long way to go before anyone could be satisfied with the way that site is being treated," Abbott said. "It's more like a garden cleanup than a forensic investigation. This is completely unacceptable."

Emotions ran high in the Netherlands, where prosecutors opened a war crimes investigation and Prime Minister Mark Rutte told parliament his government's priority was to recover and identify the bodies of the passengers.

"It is clear that Russia must use her influence on the separatists to improve the situation on the ground," Rutte said.

ALL OPTIONS

"If in the coming days access to the disaster area remains inadequate, then all political, economic and financial options are on the table against those who are directly or indirectly responsible for that," he said.

Putin, in a televised address, said the downing of the airliner must not be used for political ends and urged separatists to allow international experts access to the crash site.

The U.N. Security Council is scheduled to vote on Monday on a resolution that would condemn the downing of the plane, and demand that those responsible be held accountable and that armed groups not compromise the integrity of the crash site.

European Union foreign ministers are due to meet on Tuesday and could announce more sanctions. Britain is pushing for tougher measures, and Italy said it expected a "strong and unified response".

But the most the EU is expected to do on Tuesday is to speed up implementation of sanctions against individuals, and possibly companies, agreed in principle last week before the plane was brought down.

U.S. CASE

Ukraine said it was willing to hand over coordination of the crash investigation to international partners, perhaps led by the Netherlands, but that Kiev was convinced the plane was shot down by "professionals".

"At the moment, we have no doubt that the plane was shot down. The reason for it - a missile strike most likely from a BUK-M1 (SA-11 radar guided missile system)," Prime Minister Arseny Yatseniuk told a news conference.

"It is clear that this system could not be operated by drunk pro-Russian terrorists. There were professional people."

Kerry said the United States had seen supplies moving into Ukraine from Russia in the last month, including a 150-vehicle convoy of armored personnel carriers, tanks and rocket launchers given to the separatists.

It had also intercepted conversations about the transfer to separatists of the Russian radar-guided SA-11 missile system, which it blames for the Boeing 777's destruction.

(Additional reporting by Peter Graff in Hrabove, Pavel Polityuk, Natalia Zinets andElizabeth Piper in Kiev, Jim Loney, Doina Chiacu, Ayesha Rascoe and Mark Hosenball in Washington, Michelle Nichols at the United Nations, Allison Lampert in Montreal, Lincoln Feast and Jane Wardell in Sydney, William James in London and Nicholas Vinocur in Paris; Writing by Giles Elgood; Editing by David Stamp and Philippa Fletcher)