Rubio, who is also President Donald Trump's national security adviser, met the officials from the three European powers on the sidelines of their talks with Iran on its nuclear programme.

Iranian negotiators were in Istanbul early Friday for their own talks with Britain, France and Germany after Trump said a deal with Tehran was "getting close".

During his meeting at a hotel in Istanbul, Rubio met with French presidential adviser Emmanuel Bonne, Britain's national security adviser Jonathan Powell, and Guenter Sautter, foreign policy adviser to the German chancellor.

Rubio also spoke with them about the Russia-Ukraine talks -- the first direct contact in more than three years between representatives of the warring sides -- which were also taking place in Istanbul on the same day.

Earlier, the European trio had met with top Ukranian officials, including Defence Minister Rustem Umerov, Foreign Minister Andriy Sybiga and top presidential aide Andriy Yermak.