One of Ireland's most senior EU civil servants has been appointed as the European Union's new ambassador to Washington.

David O'Sullivan has been working as the chief operating officer of the EU's foreign service arm, the External Action Service.

He takes over from Portuguese official Joao Vale de Almeida at a time of heightened transatlantic diplomatic activity over Ukraine and over the EU-US trade negotiations.

Mr O'Sullivan has previously been director general of the European Commission's trade division and the top civil servant at the commission.

The 61-year-old graduate of Trinity College was first seconded to Brussels from the Department of Foreign Affairs in 1979.

He later served in the cabinets of commissioners Padraig Flynn and Peter Sutherland.

Mr O'Sullivan's expertise as a former head of the commission's trade division is seen as a key reason for his appointment.