Boris Johnson's words came at a reception for editors and executives at newspaper publisher Archant London, according to reports confirmed by City Hall.
Johnson is understood to have said he would fight against London boroughs launching more publications at the expense of council taxpayers and the local press.
Archant London MD Enzo Testa, who was present at the meeting, said: 'I am sure we left Johnson with a better understanding of some of our real concerns, not least of which is the growth of taxpayer-funded council papers.'
One of the first moves made by Johnson when he took office was to axe the Greater London Authority's own newspaper, The Londoner. However, many of London's boroughs maintain their own council publications.
Separately, the Audit Commission has declined to investigate the impact of council publications on the local media.