Google, the search giant, has said it will introduce new types of online advertisements in an attempt to increase revenues at YouTube, the video-sharing website it owns.

Eric Schmidt, Google's chief executive, said that the adverts - which will appear while a person is watching a video on YouTube - would be different from previous types of video-related advertising, which has tended to appear before or after a clip.

"We have new ad products that are not pre-roll and post-roll," Mr Schmidt was quoted as saying at a conference in California, but he declined to give more details. "Think of them as ads that use the page around YouTube in interesting ways."

Google has said it wants to increase the revenue derived from YouTube, which it bought for $1.65 billion two years ago, but admits that it hasn't yet found the "breakthrough" that will enable it to roll out a widespread advertising platform without annoying users of the site.

"We're working but have not yet in my view gotten a breakthrough around monetisation," Mr Schmit said in a CNBC interview recently - adding that the company had made its YouTube strategy a top priority for this year.

The new ads would be rolled out "over the next couple of months," Mr Schmidt said.

The majority of the advertising that appears on YouTube is in the form of display adverts - banners and panels arranged around the video screen. Many appear on the channels of so-called partners, such as BBC Worldwide, which have specific agreements with Google for placing adverts on their pages.

Google allows advertisers to choose which category of video they would like their advert to appear alongside - entertainment, travel, news, politics etc. - what time of day it will appear and, in some cases, to what age of viewer it will be shown.

The company has also experimented with 'in video' advertising, where a banner advert appears across the top of the screen while a video is played and a succession of text adverts are shown across the bottom - though the reaction to these among users has been mixed.

"The experience of the viewer is paramount," Google has said of its quest to find a successful formula for placing adverts alongside video content.

In October, the company said that websites which embedded YouTube videos on their pages would for the first time be able to share in the revenue generated by advertisements attached to the videos, though the offer only applies to some YouTube content.

The adverts are placed via AdSense, the same platform Google uses to generate revenue from search queries on the web.

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