Dutch PM Mark Rutte says experts have arrived in Torez in Ukraine, where the remains of victims of the Malaysia Airlines plane crash are being stored.
The three Dutch forensic scientists are aiming to start work on identifying the 196 bodies stored there on trains.
Pressure is growing on pro-Russian rebels to allow experts to the crash site some 15km (9 miles) away.
The US says there is growing evidence of Russian complicity in the downing of the plane last week.
All 298 people on flight MH17 died when it was reportedly hit by a missile.
Russia has been accused of providing the rebels with an anti-aircraft system that was allegedly used in the attack on 17 June. It denies the allegations.
Mr Rutte, whose country lost 193 people, warned Russia on Monday that all political and economic options were on the table if access to the crash site remained unsatisfactory. "We want our people back," he said in parliament in The Hague.
Natalia Antelava is handed passenger documents by volunteers at the crash site: "It shows you how badly organised it is... they don't know who to give this to"
In other developments on Monday:
- Ukrainian officials say 272 bodies have so far been found
- Ukrainian PM Arseniy Yatsenyuk proposes that the Netherlands will lead an international investigation
- Heavy fighting is reported on the streets of Donetsk - the main-rebel held city
- Russian President Vladimir Putin says it is essential to give international experts complete security so they can conduct an independent investigation
The Dutch experts are the first international investigators to arrive closer to the crash site since the plane went down.
Monitors from the Organisation for Security and Co-operation in Europe (OSCE) have been at the accident site, but their access to the wreckage has been limited by the rebels.
On Sunday, the remains of up to 196 plane victims were loaded on to refrigerated rail wagons in Torez. A second train arrived there later.
Ukrainian officials say 272 bodies have now been found at the crash site 
Tough negotiations are continuing about moving the train with the bodies from the rebel-held area Negotiations are continuing between the authorities in Kiev and the rebels for the trains to be allowed to leave for government-held territory for identification and analysis.
Australia's Foreign Minister Julie Bishop earlier called on pro-Russian separatists not to use the bodies as pawns in their conflict with the Ukrainian authorities.
"There are 298 bodies on that site - their families, their loved ones want them home now," she said.
Separately, US Secretary of State John Kerry the US had seen major military supplies moving into Ukraine from Russia in the last month, including a convoy of armoured personnel carriers, tanks and rocket launchers.
John Kerry: "The lack of access makes its own statement about culpability and responsibility".
Intercepted calls suggested a Russian SA-11 missile system - also known as BUK - had been transferred to the rebels, Mr Kerry said, and the US had seen a video of a launcher being moved back into Russia after flight MH17 crashed.
"There's [an] enormous amount of evidence that points to the involvement of Russia in providing these systems, training the people on them," Mr Kerry said on a US TV network.
He also threatened further sanctions on Russia and called on European allies to get tougher with President Putin after the "wake-up call".
Meanwhile, UK Prime Minister David Cameron said Europe and the West "must fundamentally change our approach to Russia" if Mr Putin "does not change his approach to Ukraine".
'Site compromised'The rebels say they will hand over MH17's flight recorders to the International Civil Aviation Organization but the US state department said rebels had tampered with other potential evidence.
Heavy machinery could be seen moving plane debris around at the crash site on Sunday.
Footage appears to show one of the plane's data recorders being moved
A Malaysian team of 133 officials and experts, comprising of search and recovery personnel, forensics experts, technical and medical experts have also arrived in Ukraine.
But the government in Kiev says it has been unable to establish a safe corridor to the crash site for the group.
Fighting remains ongoing in eastern Ukraine between the separatist rebels and government forces in a conflict which erupted in April and is believed to have claimed more than 1,000 lives.
The passenger list released by Malaysia Airlines shows the plane was carrying 193 Dutch nationals, including one with dual US nationality.
Other victims included 43 Malaysians (including 15 crew), 27 Australians, 12 Indonesians, 10 Britons, four Germans, four Belgians, three from the Philippines, and one from both Canada and New Zealand.
Have you been affected by this story? You can send us your experiences by emailing haveyoursay@bbc.co.uk using the subject line "Malaysia plane".
Dutch experts arrive in MH17 inquiry
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