Google has responded to major companies withdrawing online adverts by promising to take "a tougher stance on hateful, offensive and derogatory content".
Philipp Schindler, the firm's chief business officer, said Google would also tighten advertising safeguards.
He added that as well as removing content, its YouTube team would revisit the guidelines on allowable videos.
The move came after several firms withdrew their ads when some appeared next to extremist content on YouTube.
Several high profile companies, including Marks and Spencer, Audi, RBS and L'Oreal, have pulled online advertising from YouTube, which is owned by Google.
In a blog post, Mr Schindler said: "Anyone with a smartphone can be a content creator, app developer or entrepreneur.
"Google has enabled millions of content creators and publishers to be heard, find an audience, earn a living or even build a business.
"We have a responsibility to protect this vibrant, creative world - from emerging creators to established publishers - even when we don't always agree with the views being expressed.
"But we also have a responsibility to our advertisers who help these publishers and creators thrive."
He added: "We have strict policies that define where Google ads should appear and in the vast majority of cases, our policies and tools work as intended. But at times we don't get it right.
"Recently, we had a number of cases where brands' ads appeared on content that was not aligned with their values.
"For this, we deeply apologise.
We know that this is unacceptable to the advertisers and agencies who put their trust in us. "
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.
Last week, ministers summoned Google for talks at the Cabinet Office after imposing a temporary restriction on the government's own adverts, including for military recruitment and blood donation campaigns.
Mr Schindler added that Google would be "hiring significant numbers of people and developing new tools....to increase our capacity to review questionable content for advertising".