Google's European boss has apologised after adverts from major firms and government agencies appeared next to extremist content on its YouTube site.
It came after Marks and Spencer became the latest firm to pull its online ads over the issue, joining others such as Audi, RBS and L'Oreal.
Google's European chief, Matthew Brittin, promised to review the firm's policies and strengthen enforcement.
But some questioned the company's commitment to tackling the issue.
A recent investigation by the Times found adverts from a range of well-known firms and organisations had appeared alongside content from supporters of extremist groups on YouTube's video site.
An advert appearing alongside a video earns the poster about £6 for every 1,000 clicks it generates, meaning brands may have unwittingly contributed money to extremists.
The Times said that rape apologists, anti-Semites and hate preachers were among those receiving payouts.
Analysis: Rory Cellan-Jones, BBC technology correspondent
There are two difficult issues for Google here - spotting videos that are illegal and should be removed from YouTube, and determining which are legal but not suitable for advertising.
Pressed by reporters on whether the firm would employ people to actively hunt down extremist videos, Matt Brittin was evasive, indicating that a combination of smart technology and user alerts to harmful content was a better option.
But his main challenge will be in providing more clarity to customers when it comes to deciding which videos are "ad-safe".
Drawing the line won't be easy - as he pointed out, news organisations put a lot of disturbing content online but need to earn money from advertising if they are to continue to invest in journalism.
Mr Brittin seems confident that by having a thorough look at its policies and showing advertisers how they can control where their messages appear, Google can regain their confidence.
But the company, which insists it's a technology platform not a media business, is finding it ever harder to hold that line.
Media firms face tight regulation - and that is what may be coming Google's way if it doesn't clean up its act.
More:
http://www.bbc.co.uk/news/business-39325916
