Donald Trump’s ex-campaign chief paid a secret group of former senior European politicians to lobby on behalf of the pro-Russian government of Ukraine, according to US special counsel Robert Mueller.

Mr Mueller, who is leading the probe into possible collusion between Russia and the Trump campaign, made the allegation in a court filing which brought new charges against Paul Manafort, Mr Trump’s 2016 campaign chairman.

Mr Manafort “retained a group of former senior European politicians to take positions favourable to Ukraine, including by lobbying in the United States,” according to the indictment.

The group was nicknamed the “Hapsburg Group” after the former Austrian royal family which dominated Europe for hundreds of years.

Mr Manafort allegedly ran the group in 2012 and 2013 while working as a consultant to Victor Yanukovych, the pro-Russian Ukrainian president who was ousted from power during the 2014 Ukrainian Revolution.

The court filing alleges that the group was “managed by a former European Chancellor, Foreign Politician A”. It does not name the politician.

The indictment does not name other members of the group or say how many former politicians were involved. But it alleges that Mr Manafort paid them more than 2 million euros for their services.