Malaysia Airlines flight MH17 broke apart over Ukraine due to impact from a large number of fragments, the Dutch Safety Board said on Tuesday, in a report that Malaysia's prime minister and several experts said suggested it was shot down from the ground.

The crash over pro-Russian rebel-held territory in eastern Ukraine on July 17 killed 298 people, two thirds of them from the Netherlands.

Ukraine and Western countries accuse the rebels of shooting it down with an advanced, Russian-made missile. The main rebel leader repeated earlier assertions that his forces did not possess such weapons.

The report said MH17 crashed due to a "large number of high-energy objects" penetrating the fuselage. "There are no indications that the MH17 crash was caused by a technical fault or by actions of the crew," it said.

Although the report did not mention a missile, impact with a large number of fragments would be consistent with a "proximity" warhead, designed to explode in the air and hurl shrapnel at its target, said Tim Ripley, a defense analyst with Jane's Defense Weekly magazine.

Such warheads can be fitted to a number of missiles, including the Russian-made BUK surface-to-air missile that Ukraine and Western allies, including the United States, say was fired by separatists who probably hit the airliner by accident.

"The preliminary report suggests that high energy objects penetrated the aircraft and led it to break up midair," Malaysian Prime Minister Najib Razak said in a statement. "This leads to the strong suspicion that a surface-to-air missile brought MH17 down, but further investigative work is needed before we can be certain," he added.

Dutch Prime Minister Mark Rutte said it was still too early to assign blame: "We need to be careful not to draw conclusions too quickly," he told journalists. "Step-by-step, the experts are working to reach irrefutable conclusions."

A final report by the board is not expected until mid 2015. The Netherlands is also running a separate investigation into the possibility of criminal charges against suspected culprits.

Russian authorities have suggested in the past that other theories were possible, including that the plane may have been shot down from the air. However, the report found no military aircraft in the vicinity.

"It's consistent with a hit by a ground missile," said Joris Melkert, a lecturer in aerospace engineering at the Technical University of Delft. "What could cause a pattern of high velocity particles 10 kilometers up in the sky? As far as I can see, the only thing that could do that is a rocket," he said. "The report finds there were only three other aircraft in the vicinity: two Boeing 777s and one Airbus A330, so both civilian, which makes the surface-to-air missile more likely."

WAR ZONE

The investigation has been hard because the crash took place near the front line. Although a small number of Malaysian inspectors and Dutch body recovery experts reached the site, fighting kept Dutch air crash investigators away. A ceasefire this week means the area is quieter at last.

"In the beginning they were all coming here, the Dutch, the Malaysians, but then they stopped because of the fighting," said Vasily, a retired miner, near the site on Tuesday. "Now it's the ceasefire and things have calmed down here a lot."

Most of the wreckage is still lying in Ukrainian wheat and sunflower fields. Passenger seats, suitcases, clothing, toys, and bags of mail were still scattered across the rolling fields around Grabovo village on Tuesday.

Large parts of the aircraft, including a big piece of wing, still lay in the open, along with flowers laid by residents to honor the dead. Bits of fuselage - some torn apart, some burned, some melted from the intense heat of the crash - lay several hundred meters away, with landing gear and engine parts.

Photographs of the wreckage detailed in the report showed multiple shrapnel impacts. A site visit would greatly help the investigation, said Tjibbe Joustra, head of the Safety Board.

"There are elements we are interested in. The cockpit is very important because a lot of those objects penetrated the cockpit," he said, adding that flight instruments also contain data not registered by the flight data recorders.

The early findings were based on data retrieved from the cockpit voice recorder, the flight data recorder, satellite and other images, and radar information. Joustra said investigators had found no evidence of tampering with the flight recorders, which were recovered by rebels and turned over to Malaysia. Kiev and its Western allies, including the United States, say separatists were supplied from Russia with a BUK, an advanced system with large missiles that have enough range to hit an airliner at cruising height.

The separatists have mostly denied ever possessing such missiles, although one separatist leader told Reuters in July that they did in fact have one on the day the plane was shot down. Moscow denies supplying the rebels with weapons.

"I can say only one thing. We just don't have the (military) equipment which could bring down a passenger Boeing, including this Malaysian plane," Alexander Zakharchenko, leader of the rebel self-declared Donetsk People's Republic said on Tuesday.

U.S. President Barack Obama said the day after the crash that "evidence indicates that the plane was shot down by a surface-to-air missile that was launched from an area that is controlled by Russian-backed separatists inside of Ukraine".

The Dutch report is "an initial, provisional sequence of events" and it could take up to a year for a final report to be concluded, the board said.

Nearly two months after the crash, Tuesday's release is several weeks past a 4 week timeframe generally required by the International Civil Aviation Organization. Extra time was given due to the complex nature of the MH17 case.

(Reporting by Anthony Deutsch; Additional reporting by Thomas Escritt and Peter Graff; Editing by Peter Graff)