Facebook plans to launch a new service that will enable the social network website's 60m users to chat with each other online.

The service, which is expected to roll out sometime in the next few weeks, represents Facebook's latest challege to AOL, Microsoft and other makers of popular instant messaging programmes.

It is likely to come as a blow to software developers who have been working on chat services designed to run on Facebook's popular application platform.

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Matt Cohler, Facebook's vice-president of product management, said: "Chat is something we think is part of the core of what's going on at Facebook."

Facebook's chat service will be more limited than many existing chat programmes. For example, it will only allow chats to take place between individual Facebook members. It will not support chats between multiple friends, or chat with friends who do not have a Facebook account.

Nevertheless, the fact that it will come free of charge and will be included as a feature of the Facebook website makes it likely to cut into the traffic on instant messenger services offered by AOL, Microsoft, Yahoo and other technology companies.

The new service is also likely to take traffic from a handful of chat applications that have been developed for use on Facebook since the site opened up to outside developers last year.

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Facebook yesterday defended the intrusion on to some of its developers' turf, arguing that users would retain the option of using a rival chat service, if they preferred.

Mr Cohler said: "We develop our applications at parity with other developers. Users can remove any of our applications if they want and swap in another feature instead."

Separately yesterday, Facebook unveiled a handful of new privacy features designed to make it easier for users to control who gets to see the information they upload to the Facebook website.

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The enhanced privacy controls come as Facebook tries to close a chapter on Beacon, a controversial advertising technology that it launched last year.

Beacon, which sends messages when users purchase products or take other actions on outside web sites, was launched to great fanfare in November but was soon hit by a privacy backlash.