The west is imposing "illegal, unreasonable and counter-productive" sanctions against Russia based on internet forgeries that do not prove any of its missiles shot down the Malaysian airliner, the Russian ambassador to London has said.

Shortly before the European Union announced further sanctions against individuals and businesses linked to the Kremlin on Thursday night, Alexander Yakovenko condemned the trade restrictions that have already been imposed and warned that any more "may well trigger a long anticipated endgame of the present global crisis".

The EU agreed at a meeting on Thursday to add 15 people and 18 companies or other organisations to the bloc's sanctions list for undermining Ukraine's territorial integrity, diplomats said. But they failed to reach agreement on economic sanctions and will resume discussions on Friday, they added.

Philip Hammond, the foreign secretary, has joined the US and Ukraine in saying there is strong reason to believe the Malaysian airliner was shot down by pro-Putin separatists using a Soviet-era Russian-made Buk missile, killing 298 people.

On Thursday night, the US state department said it had evidence Russia intended to deliver "heavier and more powerful" rocket launchers to separatists in Ukraine.

However, Yakovenko said Russia had never given weapons to the separatists.

"The ample proof of inconsistencies of the initial narrative by Kiev and Washington has been provided by the closed briefing by the American intelligence officials on Tuesday," he told journalists at the Russian embassy in London.

"I took this from British media. Given media reports, there was nothing convincing, not to say compelling, in those materials.

"The case, as is admitted, is built upon photos and messages from social media sites, placed by Ukrainian authorities and since then proved to be forgeries, as ambassador Churkin demonstrated at the UN security council meeting. Naturally, our American partners say that they have no way of certifying the authenticity of those materials."

He added: "What we do is providing humanitarian assistance and receiving refugees from Ukraine in our territory. I don't have to say that people in Russia entertain strong feelings over the atrocities committed today by the Ukrainian forces against civilians, their ruthless use of heavy weapons and air force to shell and bomb [a] peaceful population."

The ambassador said the war in Ukraine had created "murky waters which are a fertile ground for all sorts of incidents".

The separatists are continuing to hold the site of the accident, but the black boxes from the plane and some of the bodies of those who died in the crash have now been released.

Yakovenko's warnings came after Boris Johnson, the mayor of London, suggested sanctions should only be directed at people in the entourage of Putin, rather than Russian business in general. He also warned people not to "lash out" against all Russians.

Johnson previously expressed unease about being asked to play tennis with the wife of a former finance minister of Putin, along with David Cameron, in return for a £160,000 donation. However, he claimed sufficient checks on the donor have now been carried out to satisfy him that the couple are not "buddies" of Putin.

"We have got to target the people who really count in Vladimir Putin's immediate entourage, in his regime, the people who are this cronies," Johnson told LBC 97.3.

"That's sensible. People say this will affect London, [that] it will do damage [but] I don't believe it will, because what people will see is a city that knows the difference between right and wrong. I think it is to the credit of Britain and to London that we are able to do these difficult things.

"I would stress obviously this is not the context for a general lashing out against all Russians, everybody who happens to speak Russian. This is a city that welcomes people from all around the world and there are many Russians here in London who are by no means buddies of Vladimir Putin."

The mayor's defence of the tennis match comes after the Conservatives were put under scrutiny over hundreds of thousands of pounds in donations from Russians, who Labour said were bankrolling their general election campaign.

An analysis by the Guardian shows more than £161,000 has come from donors with links to the Kremlin's business interests in the last five years.

It also emerged that one of Cameron's trade envoys, Charles Hendry, is president of a pro-Russia business lobby group whose advisory council includes an ally of Putin who recently struck an oil deal with Syria's Bashar al-Assad, and a former chief of the arms company that designed Buk missiles.

The UK and some eastern European countries have been pushing for sanctions not just on individuals and businesses linked to Putin's regime but for some wider sectoral restrictions that could hit trade in areas such as energy, defence and finance. The list of individuals who face sanctions announced on Thursday is likely to be published on Friday or Saturday.

Simon Jenkins, page 35