The Trump administration downgraded the diplomatic status of the European Union last year, in the latest sign of deteriorating relations between Washington and Brussels.

The European Union’s delegation in Washington – led by Irishman David O’ Sullivan – had enjoyed the same status as a national embassy. But the State Department last year classified the embassy as an international organization, alongside the African Union.

Mr O’Sullivan, who is due to finish his term as EU ambassador in the first half of this year, is the second Irish citizen to hold the position, following John Bruton’s tenure from 2004 to 2009.

According to reports, the State Department did not inform the European Union of the reclassification. Instead, it became apparent when Mr O’Sullivan’s name was not called in the usual order in keeping with diplomatic protocol at the funeral of George HW Bush last month.

German newspaper Deutsche Welle was the first to carry the story.

The EU delegation in Washington plays a central role in co-ordinating policy between the 28 EU member states, with Mr O’Sullivan regularly meeting EU ambassadors. The recent decision by the Trump administration to lift sanctions on Russian energy giant Rusal, the owner of Aughnish Alumina in Limerick, for example was a result of intensive behind-the-scenes lobbying by not just Irish officials but also the EU embassy in Washington.

The development emerged as EU trade commissioner Cecilia Malmstrom arrived in Washington this week for talks with US trade representative Robert Lighthizer. The meeting between the two top trade representatives is expected to lay the groundwork for more formal negotiations in the coming weeks amid continuing trade tensions between Brussels and Washington.

The US president, who has long complained about America’s trade deficit in goods with the European Union, refrained from imposing tariffs on European cars following a July meeting with European Commission president Jean-Claude Juncker. But he remains skeptical of the bloc nonetheless.

He made no secret of his view of the European Union during the presidential campaign, voicing support for Brexit on several occasions. The EU is just one of several multilateral institutions such as Nato and the UN that the Trump administration has dismissed. Last month US secretary of state Mike Pompeo delivered a speech in Brussels that was highly critical of the European Union, calling for the restoration of the role of the nation-state in the liberal international order.