Michael Flynn, President Donald Trump's former national security adviser, has confirmed his lobbying firm carried out $530,000 worth of work that may have helped the Turkish government in the run-up to the US election.

Mr Trump sacked Flynn, a former US army lieutenant-general, last month for misleading Vice President Mike Pence about the extent of his contacts with Russia's ambassador to the US, Sergey Kislyak.

In the latest development a lawyer for Mr Flynn filed documents with the US Department of Justice registering him as a "foreign agent" over work on behalf of a Turkish company.