Washington warned Russia on Sunday it was risking its long-term relationship with the US and other members of the international community by failing to halt what was described as aggression against the US-backed government in Georgia.

Tough exchanges in the United Nations Security Council and equally tough messages from the White House and Moscow suggested the Georgia crisis had brought relations to their lowest point in years after a series of diplomatic spats over a range of issues.

Events in Georgia also marked the most serious international crisis of the US presidential campaign, highlighting differences between Barack Obama and John McCain, who on Sunday accused his Democratic rival of “siding with the Kremlin”.

The dispute between the two campaigns came as the White House warned that the “dangerous escalation” of conflict beyond the Georgian separatist province of South Ossetia could have a “significant long-term impact on US-Russia relations”.

In Beijing, where he is attending the Olympic Games, George W. Bush, US president, said: “The attacks are occurring in regions of Georgia far from the zone of conflict in South Ossetia. They mark a dangerous escalation in the crisis.”

In heated exchanges at the Security Council, Zalmay Khalilzad, US envoy, suggested Moscow’s military campaign that began in South Ossetia was aimed at unseating the democratically elected government of Mikheil Saakashvili, Georgia’s president.

“The days of overthrowing leaders by military means in Europe is over,” he said.

His Russian counterpart, Vitaly Churkin, countered that “regime change” was a “purely American invention. We are all for democracy in Georgia”.

The Security Council met in emergency session for the fourth time in three days as the focus of the conflict spread to separatist Abkhazia, with the US and other western states meeting later in the day to draft a formal UN ceasefire resolution that would, in part, condemn Russia’s actions.

Ban Ki-moon, UN secretary-general, said he was “profoundly concerned” that the violence had spread from South Ossetia to Abkhazia. The UN has an observer mission in Georgia to monitor a previous ceasefire with Abkhazia, and the situation there is already on the council’s agenda for further action via a formal resolution.

Irakli Alasania, Georgian ambassador, who requested the council session jointly with the US, called for immediate diplomatic and humanitarian intervention in response to what he called Russian aggression and occupation of Georgian territory.

Parrying allegations that Russians were involved in the separatist unrest in South Ossetia, Mr Churkin said that more than 100 US military advisers were assigned to the Georgian authorities during an arms build-up by Tbilisi.

That, coupled with a recent visit by Condoleeza Rice, US secretary of state, and recent joint US-Georgian military exercises might have prompted Tbilisi to believe it had support in its attempt to reassert its authority over South Ossetia, he said.

Sergei Markov, a member of the pro-Kremlin United Russia party, said he believed Mr Saakashvili would not have launched the attack without encouragement from the US administration.

He said Kiev’s threat that it would bar Russian warships from returning to their port in Sevastopol raised the risk that the conflict could spread to Ukraine.

Washington has stood staunchly behind Mr Saakashvili, who is intent on integrating his country into the European Union and joining Nato. But, however dismayed the US administration might be by Russia’s military action, there is little it can do to reverse the course of events that seem likely to lead to Georgia’s loss of control over separatist regions.

Martha Olcott of the Carnegie Endowment for International Peace said there were few instruments the west could apply against Russia without harming itself. “A trade embargo against Russia would be like cutting off your nose to spite your face because of the west’s dependence on Russian oil and gas,” she said.

As the crisis escalated over the weekend, both US presidential candidates spoke about Mr Saakashvili. Mr McCain, who this year said he would eject Russia from the Group of Eight leading industrial economies were he to become president, responded angrily to a statement by the Obama campaign that highlighted the role of Randy Scheunemann, Mr McCain’s chief foreign policy adviser, in having previously lobbied for the Tbilisi government.

Mr Obama issued a new statement condemning more strongly Russia’s actions in Georgia, following a moderately worded version produced on Friday. But the McCain campaign said that Mr Obama’s statements demonstrated poor judgement.

“Today many are dead and Georgia is in crisis, yet the Obama campaign has offered nothing more than cheap and petty political attacks that are echoed only by the Kremlin,” it said.

Additional reporting by Catherine Belton and Isabel Gorst in Moscow, Roman Olearchyk in Tbilisi and Quentin Peel in London

Copyright The Financial Times Limited 2018. All rights reserved.

Comments have not been enabled for this article.