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The EU and US are in trade talks worth €120bn, though it is against the backdrop of the Ukraine crisis and the NSA spying scandalReuters

A fourth round of trade talks between the US and European Union worth €120bn are underway amid an awkward atmosphere because of the Ukraine crisis and NSA snooping scandal.

The discussions, which started in July 2013, are aimed at establishing the Transatlantic Trade and Investment Partnership (TTIP) to break down any trading barriers. This set of talks will end on 14 March.

But there are tensions between the EU and US. It emerged during 2013 that the NSA, a US security agency, had spied on some EU leaders and officials, including German Chancellor Angela Merkel.

Documents showing the extent of the NSA's activities were leaked by the agency's whistleblowing former contractor Edward Snowden.

There has also been some disagreement between the EU and US over how to handle the Ukraine crisis.

A largely pro-west revolution ousted Viktor Yanukovich, Ukraine's Russia-allied president.

Russian troops have since entered Crimea, a semi-autonomous region of Ukraine with a large population of ethnic Russians and Russia-owned industry.

Vladimir Putin, Russia's president, claims this is to protect Russians in Crimea and maintain peace in Ukraine. He has attacked the revolution as the work of fascists.

Both the EU and US have criticised Putin, saying entering Crimea is an act of aggression that infringes national sovereignty.

But there was embarrassment for the US when the country's Assistant Secretary of State Victoria Nuland was caught on tape saying "f**k the EU" because of frustration over how it was handling the Ukraine crisis.

The EU relies on Russia for a significant chunk of its gas supplies and so has been cautious in its criticism because it has a lot more to lose than the US.

However the two agreed to co-ordinated visa sanctions for Russians and the EU has halted investment talks with the state – though Brussels stopped short of any formal trade curbs.