In response, Sidyakin wrote on Twitter: "It's an eye for an eye, a ball for a ball - don't let the USA take part in the 2014 World Cup - end their membership of FIFA," before citing past "aggressive action" against Yugoslavia, Iraq and Libya as well as their attempts to "encroach" on Syria, as justification. 

Sidyakin represents the United Russia party, the largest in the country and closely associated with President Vladimir Putin, while Markelov is a member of the far-right Fair Russia party although, like Kirk and Coates, neither individual has a particularly high-profile.

But in recent months tension between the two countries has been played out in a sporting arena, and has involved the highest authorities in each country.

The US beat Russia 8-0 in a women's friendly match in Atlanta last month, while the men's sides last crossed paths in a 2-2 friendly draw in November 2012 ©Getty Images

Following much criticism of an anti-gay rights propaganda law introduced into the Duma in 2013, US President Barrack Obama chose not to attend Sochi 2014 and sent instead a delegation led by three openly gay figures, former tennis player Billie Jean King, two-time Olympic ice hockey medallist Caitlin Cahow, and skating champion Brian Boitano.

There was also consternation in the US during the Games after one of the two final Olympic Flame lighters, former three-times Olympic figure skating champion Irina Rodnina, was allegedly found to have posted racist messages about Obama on Twitter.

Although a visit by Putin to the US House during the Games seemed to have cooled tensions, Russia's subsequent intervention in Ukraine has revived tensions, with no US delegation attending the ongoing Paralympic Games in Sochi. 

But while each letter gives a further glimpse of each nation's views of the other, FIFA membership and the World Cup seemed an unlikely backdrop for further tension and, although they are yet to comment, it seems very unlikely FIFA will act upon either letter.

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