EU and US warn Russia against 'humanitarian' invasion of Ukraine

His office said in a statement on the call with Merkel: “The two leaders agreed that any Russian intervention in Ukraine, even under purported 'humanitarian' auspices, without the formal, express consent and authorisation of the government of Ukraine is unacceptable, violates international law, and will provoke additional consequences”.

Merkel in her own communique noted that any Russian intervention must have Ukraine’s consent.

Cameron’s office added that: “The international community should impose further, tougher sanctions if Russia pursues such action”.

The warnings come after Russia floated a proposal for sending in humanitarian aid convoys earlier last week at a meeting of the UN Security Council in New York.

The US ambassador to the UN, Samantha Power, said at the time that if Russian troops openly cross the border it “would be viewed as an invasion of Ukraine”.

US vice president Joe Biden, following a call with Ukraine president Petro Poroshenko also at the weekend, added: “If Russia were serious about improving the humanitarian situation in eastern Ukraine, it [should] immediately stop its shelling of Ukrainian troops and release Ukrainian hostages being held inside Russia, as well as cut its provision of weapons to Russian proxies operating in Ukraine”.

The EU in July already imposed economic sanctions on Russia, including a ban on purchasing of long-term debt by its top banks and on EU exports of high-end oil drilling technology.

But leaked EU options papers on further restrictive measures indicate that European states have made preparations to go much further if need be, with “high intensity” proposals including a blanket ban on EU investments in Russia as well as an oil and gas embargo.

Russia last week hit back with a ban on imports of EU food which the European Commission says could cost the bloc up to €12 billion in lost trade.

The office of French president Francois Hollande over the weekend said EU institutions are to make sure the "consequences of the embargo are accurately assessed and measures appropriate to the situation are taken”. It added that “special attention will be paid to producers of fruits and vegetables”.

It also echoed Poland in saying the EU is likely to seek redress against Russia using World Trade Organisation (WTO) mechanisms.

“These massive violations by Russia are sufficiently large to threaten it with expulsion from the WTO”, Polish agriculture minister Marek Sawicki told the Gazeta Wyborcza daily.

Individual EU countries are already counting the cost of the Russian ban, with analysts saying it is likely to see a drop in the price of milk and fisheries products in Europe, as well as a hike in the prices of imported meat as Latin American exporters increase shipments to Russia.

Roberto Moncalvo, the head of Italy’s Coldiretti group, told AFP that Russia has already sent back container loads of Grana Padano parmesan cheese.

The Danish Agriculture and Food Council has estimated the Russian ban will cost its members €469 million. Germany has estimated its likely losses at up to €1.6 billion, while Poland has asked the US to open its markets to exports of Polish apples to help compensate.

“There is a greater understanding on account of the fact that the United States has also been hit by Russian sanctions," Poland’s ambasador to the US, Ryszard Schnepf, told Polish press agency Pap.