The European Union ruling that US tech giant Apple must pay €13bn (£10.9bn, $14.50bn) in back taxes was clearly based on facts and existing rules and not an action taken "against the United States of America", EU Commission President Jean-Claude Juncker said on Sunday.

Speaking ahead of the G20 summit in China, Juncker confirmed the Commission's investigations had mainly targeted European companies and had not singled out the tech giant.

The remarks were aimed at reassuring US lawmakers following the Commission's ruling on 30 September, that tax arrangements between Ireland and the US firm broke EU laws on state aid.

Analysts are now warning of transatlantic discord, with US lawmakers concerned the result represents a European encroachment on the US potential tax base.

Speaking on Saturday, Director of the OECD Center for Tax Policy and Administration Pascal Saint-Amans called Apple's tax planning "outrageous" but confirmed the ruling was in line with current regulations.

However, Saint-Amans said he believed it would be unlikely to serve as a precedent for enforcement on future income earned by multinationals.

Both Ireland's finance minister and Apple have said they intend to appeal the EU's ruling.

Tim Cook, Apple's chief executive Tim Cook, described the ruling as "total political crap", but France and Germany backed Brussels' decision.

Margrethe Vestager, the European Commissioner for competition, said the sweetheart deal had enabled Apple to pay substantially less tax than other businesses over many years.

She said: "This selective treatment allowed Apple to pay an effective corporate tax rate of 1% on its European profits in 2003 down to 0.005% in 2014."

The tax penalty, the largest ever to be handed out, is the latest in a string of high-profile tax crackdowns on multinationals, spearheaded by the Paris-based Organization for Economic Cooperation and Development (OECD).

Online giant Amazon and fast-food chain McDonald's face similar EC probes over taxes they pay in Luxembourg, while coffee chain Starbucks has been ordered to pay up to €30m to the Dutch state.

European Commission chief Jean-Claude Juncker has said the European Commission's ruling over Apple's tax bill is in line with EU laws John Thys/ AFP