Apple plans to showcase a 3G iPhone and a new Leopard operating system to developers in San Francisco next month.

The company revealed today that development tools for the smartphone and the OS would be the focus of the company's annual World Wide Developers Conference (WWDC) in June.

The WWDC allows Mac developers to speak with Apple engineers on current and upcoming products. The sessions are closed to the press and attendees are held to non-disclosure agreements.

The only event open to the media is the keynote session usually given by chief executive Steve Jobs.

Jobs has traditionally used the platform to make major announcements regarding Apple and the Mac OS in particular.

Last year, Jobs used the keynote to announce a Windows version of the Safari web browser and to say that the iPhone would initially be limited to web applications.

This year's address is also anticipated to bring major news relating to the iPhone.

Jobs said last year that a 3G version could be released in 2008, and a recent price drop and rash of sell-outs by retailers in the US and UK has fuelled speculation of a new iPhone model.

Apple did not reveal any details on the keynote, but did say that iPhone development will again be a major part of WWDC.

The company plans to devote an entire programme track to development with the new iPhone 2.0 software as well as the software development kit.

The 2008 WWDC keynote address is scheduled for 10am US Pacific time on 9 June.