Theresa May has followed up on Grant Shapps' attack on the BBC by suggesting its online dominance is damaging local newspapers.
The home secretary's warning will alarm BBC chiefs ahead of the renewal of the corporation's royal charter in 2016.
She said the claims of "a very senior individual" that the BBC's function was to open up markets for other competitors did not apply in all cases.
"I pointed out, as we have seen with BBC Online, it did not open up the market but dominate it in a way that prevents others from being able to come in and have that sort of access," she said at the Society of Editors' annual conference in London.
May said the BBC's "dominant position on the internet" - coupled with its ability to subsidise the provision of internet news via the licence fees - was partly to blame for local newspapers facing a "particularly hard time" at present.
"If the BBC can, as they do, provide all the locally significant news, what is left to motivate the local media to buy a paper?" she asked.
"It's destroying local newspapers and could eventually happen to national newspapers as well."
May said politicians could be adversely affected by the trend, because constituency MPs needed to use local media to raise issues and disseminate information about political activities.
"This is a debate that won't go away and I believe that the BBC has to think carefully about its presence locally and the impact that has on local democracy," she added.
The decline of regional journalism in Britain has left politicians frustrated. One politician told Politics.co.uk last week she relied on regional news programmes more because of a reduction in the number of local news outlets.
"No single source of news can possibly represent the variety of opinion that there is in this country and a monopoly news provider would be far too easily captured by special interests," May said.
"So competition in the provision of news is essential to democracy and diminishing competition is dangerous to the health of democratic politics.
"That's why it's important that the internet does not have the effect of making a plurality of newspapers commercially impossible in Britain."
Her comments follow a warning from Tory party chairman Grant Shapps, whose more brazen criticisms of the BBC focused on its allegedly biased left-wing reporting.
Deputy prime minister Nick Clegg spoke out against Shapps, saying the Tories could be relied on to criticise the BBC "like clockwork" in the run-up to a general election.