Twitter is trying out a new feature to display ads, or promoted tweets, directly in a user's Twitter stream, but the company admits it's watching carefully to see how people react.

The site expanded its "promoted tweets" feature yesterday, starting slowly by displaying the ads only for those who use HootSuite, a third-party Twitter client. Promoted tweets are tweets that advertisers pay to show to a large number of people, similar to the way advertisers pay for sponsored links that appear among search results at Google.

Those who access Twitter through HootSuite will begin to see ads in their timelines that Twitter is promising will be relevant to their interests and activities. Some HootSuite users may not see any ads, while others will see them pop up in different places on their timelines, according to Twitter's official blog. The appearance and frequency of the ads will depend on their relevance to each user.

Promoted tweets have been showing up on Twitter since earlier in the year. But until now they've been relegated to spots outside of a user's Twitter timeline, such as in search results or in the list of trending topics.

Realizing that some may not be happy to see ads in their timelines, Twitter said it's taking a "deliberate and thoughtful approach" to the new feature and will look carefully at how people react to and use the ads. Any that fail to engage will either be dropped or changed. Twitter is also looking at this initial rollout as a test period and will likely need to tread cautiously before it expands the feature beyond HootSuite users.

HootSuite has captured more than 900,000 users for its third-party Twitter tool and is the first company to work with Twitter on the new rollout. As part of the agreement between the two, HootSuite will get a portion of the sales, while Twitter will sell the actual ads, according to Advertising Age. Insiders at Twitter say the company will eventually deploy the ads to other Twitter users depending on how successful they are, Ad Age reported.