US President Donald Trump and Russian counterpart Vladimir Putin had another, previously undisclosed conversation at this month's G20. They spoke towards the end of a formal dinner but the White House has not revealed what was discussed. President Trump has condemned media revelations of the talks as "sick". The two leaders' relationship is under scrutiny amid allegations of Russian interference in the US election. US intelligence agencies believe Moscow tried to tip the election in Mr Trump's favour, something denied by Russia. Mr Trump has rejected allegations of any collusion.