David Cameron expressed anger about the shooting down of Malaysia Airlines flight MH17 in a telephone conversation with Vladimir Putin on Sunday as EU leaders started preparing fresh sanctions against Moscow for its alleged role in the attack.
Ten Britons died when flight MH17 was shot down with a missile on Thursday and sources indicated that Cameron was furious that it took the Russian president three days to respond to his request for a telephone conversation.
The US secretary of state, John Kerry, made the clearest accusation against Russia to date over its involvement in the missile attack, which killed 298 people.
"We have enormous input about this that points fingers," Kerry told CNN. "It is pretty clear that this was a system from Russia, transferred to separatists. We know with confidence that the Ukrainians did not have such a system anywhere near the vicinity at that point of time."
He said satellite imagery showed that "at the moment of the shootdown we detected a launch from that area. Our trajectory shows that it went to the aircraft."
Kerry added that video evidence showed a Buk missile launcher, the anti-aircraft weapon believed to have hit the airliner, being driven over the Russian border after the attack, with at least one of its missiles missing.
After the call between Cameron and Putin, Downing Street said: "The prime minister spoke to President Putin this evening and made clear that the shooting down of MH17 was totally unacceptable. The evidence suggested that pro-Russian separatists were responsible and the prime minister made clear that if Russia wants to put the blame elsewhere they would need to present compelling and credible evidence.
"The PM made clear that our priority is to get experts to the crash site so they can recover and repatriate the victims and collect any evidence necessary for the investigation. The PM emphasised that the families of 298 individuals need to know that everything is being done to make this happen and called on President Putin to use his influence on the pro-Russian separatists to ensure this happens. The delay and restrictions so far were completely unacceptable and indefensible."
There is mounting fury in the EU – and more widely – that crucial evidence is being removed and the bodies of the dead are being allowed to decompose because the separatists and their Russian allies are obstructing a full, independent investigation.
Earlier, Cameron, who will make a statement to MPs about the crisis , spoke to the Angela Merkel, the German chancellor, and François Hollande, the French president. The three leaders agreed that "the EU must reconsider its approach to Russia" and that EU foreign ministers would consider further sanctions at a meeting on Tuesday, No 10 said.
A government source said the French and German position on sanctions had shifted since last week. "They are all very clear that a plane has been shot out of the sky and that all the evidence points to it being the work of Russian separatists, and that therefore the EU should impose further measures," the source said.
In an interview on the BBC's the World this Weekend, Philip Hammond, the new foreign secretary, said a range of measures would be considered.
"Arms sales is something we need to look at," he said. "An investment ban on investment in the Crimea, sending a clear signal that we will not tolerate the illegal annexation of Crimea, broadening the number of individuals who are subject to sanctions to include the so-called 'crony group' around President Putin."
Monitors from the Organisation for Security and Cooperation in Europe, who have been in eastern Ukraine to observe the conflict between government and rebel forces, have been allowed on the scene, a few miles east of Donetsk, but specialist air crash investigators from around the world were still in Kiev on Sunday night, awaiting guarantees of safe passage to the site.
Dianne Feinstein, the head of the Senate foreign relations committee in the US, said: "The nexus between Russia and the separatists has been established very clearly." In a direct and personal challenge to the Russian premier, she added: "So the issue is, where is Putin? I would say, Putin you have to man up. You have to say this was a mistake, which I hope it was."
The Ukrainian president, Petro Poroshenko, spent the day calling western leaders to ask them to list the main rebel organisation in the east of the country, the Donetsk People's Republic (DNR), as a terrorist organisation, which would mean that any country providing support would risk being sanctioned as a state sponsor of terrorism.
In a conversation with Hollande, Poroshenko said the downing of MH17 was comparable with terrorist attacks by al-Qaida and the 1988 bombing of Pan Am flight 103.
The EU has already imposed sanctions on 72 people – both Ukrainian and Russian nationals – and two organisations for violating Ukrainian territorial integrity. One of those on the list is Igor Strelkov, the DNR's "defence minister", who Ukraine says is a serving officer in Russian military intelligence named Igor Girkin.
The toughest line at Tuesday's foreign ministers meeting in Brussels is likely to come from the British and French, but most of all from the Dutch, who have lost 192 of their citizens.
The UN security council was last night considering a draft resolution to condemn the shooting down of the plane, demand armed groups allow unfettered access to the crash site, and call on states in the region to cooperate with an investigation.
Australia despatched its foreign minister, Julie Bishop, to New York to push for a UN Security Council resolution. It is unclear whether Russia intends to veto it.
Australia – which lost 28 citizens – circulated a draft text to the 15-member security council and UN diplomats said it could be put to a vote as early as Monday.
The draft resolution "condemns in the strongest terms the shooting down of Malaysia Airlines flight MH17 ... resulting in the tragic loss of 298 lives" and demands those responsible "be held to account and that all states cooperate fully with efforts to establish accountability".
It "expresses grave concern at reports of insufficient and limited access to the crash site and of tampering with evidence related to the incident" and demands "armed groups in control of the crash site and the surrounding area refrain from any actions that may compromise the integrity of the crash site and immediately provide safe, secure, full and unfettered access."
Australia's prime minister, Tony Abbott, said that Bishop would stay at the UN "for as long as she needs to be" to get investigators access to the black box, the debris and witnesses.
"We owe it to the dead, all the dead, we owe it to the families, all the families to do everything in our power to respect the bodies, to find the truth and to ensure justice is done," Abbott said in a television interview.