KIEV, Ukraine — U.S. and European leaders piled pressure on Vladimir Putin to back down on eastern Ukraine as chaos surrounded the crash site of the Malaysian Air jet. In Kiev, the government said the missile system used by pro-Putin rebels to shoot the plane down is back in Russia.

U.K. Prime Minister David Cameron said Sunday that the U.S. and Europe must “fundamentally change” their approach to Russia. State Department spokeswoman Jen Psaki said yesterday the U.S. is “deeply concerned” about the refusal by pro- Russian rebels to provide safe and unfettered access to the crash site. On the ground, the fate of the bodies of the 298 passengers remains shrouded in confusion.

“Russia risks becoming a pariah state if it does not behave properly,” U.K. Foreign Secretary Philip Hammond said in a television interview on Sky News Sunday. “We now need to use the sense of outrage that is clear to get a further round of sanctions tightening against Russia, with further steps as well, if the Russians do not comply with the requirements that the whole international community now places upon them.”

President Putin is facing the ire of world opinion at a time when the U.S. and its allies are already trying to push him into a corner over the annexation of Crimea and his support for pro-Russian rebels in east Ukraine. The U.S. and Europe tightened sanctions last week and both Cameron and Dutch Prime Minister Mark Rutte said this weekend that Europe needs to consider further moves to bring Putin to heel.

President Barack Obama on July 18 decried what he termed Putin’s refusal to “de-escalate the situation.” While the Russian president has blamed the Ukrainian government, saying the crash wouldn’t have happened had it not fomented the conflict in the east, the administration in Kiev says it has proof that the plane was brought down by a Russian missile.

Separatists had in their possession “at least” three Russian-made surface-to-air missile systems, known by their NATO designation SA-11 Gadfly, Ukraine state security official Vitaliy Nayda said yesterday. As part of a cover-up of who fired the missile, three of the systems were transported back to Russia just hours after the plane was shot down, he said. Nayda displayed photos that he said showed them on the road to the Russian border.

The Gadfly, known locally as the Buk-M, is a radar-guided weapon that can find a target at a range of 140 miles and reach altitudes as high as about 72,000 feet, according to the army-technology.com website.

The crash site at Grabovo, less than 60 miles from the Russian border, is providing a focal point for global anger as armed rebels hover over the investigation, making the reclamation of wreckage and corpses more difficult.

With limbs and bodies still scattered around the area, governments around the world are clamoring to be allowed greater access to bring the remains home. Contradictory reports about the bodies and eyewitness accounts of rebels and local miners sifting over the victims’ possessions are also hampering an accurate inspection, said Organization for Security and Cooperation in Europe spokesman Michael Bociurkiw.

Ukrainian troops are holding their positions near the airports of Luhansk and Donetsk — both about 60 miles from the crash site — and widened the area they have under their control, the Defense Ministry said in a statement on its website. Government troops repelled all the rebels’ attacks overnight.

While the diplomatic pressure on Putin to disown the rebels and help end the conflict in east Ukraine is rising, building the political will in Europe to force him to do so may still prove difficult. The European Union relies on Russia for about 30 percent of its gas, according to European Commission data, making some countries reluctant to act.

One group of countries, which runs in an arc from Estonia in the northeast through Austria and down to Greece in the southeast, gets more than 75 percent of its gas imports from Russia.

The immediate reaction on July 19 didn’t suggest a rush to action was imminent.

Poland demanded a harder line on the Kremlin while Italy signaled no shift from its opposition to more biting sanctions. German Chancellor Angela Merkel straddled the divide, telling reporters in Berlin yesterday that the region’s response so far is “adequate” and “it is especially Russia’s responsibility for what is going on in Ukraine right now.”

“We must turn this moment of outrage into a moment of action,” Cameron wrote in the Sunday Times newspaper in London today. “This is not about military action, plainly. But it is time to make our power, influence and resources count.”