Apple unveils new iPhone 6S, 6S Plus

San Francisco

Apple on Wednesday unveiled two updated iPhones, aiming to build on the success of its large-screen handsets introduced late last year.

The new smartphones are the iPhone 6S and 6S Plus, keeping the same overall dimensions of the last version.

"They look familiar, but we have changed everything about these iPhones," chief executive Tim Cook said at a San Francisco media event.

One of the key new features is called "3D touch" which responds to pressure exerted on the screen to allow users to look inside messages and applications.

The new iPhones will use the upcoming iOS 9 operating system, which supports new features such as 3D touch.

The 6S will include the 4.7-inch (about 12-centimeter) display of its predecessor and the 6S Plus -- one of the more popular handsets in the "phablet category" -- has a 5.5-inch screen.

But the devices have more powerful processors that allow for improved graphics, and a new aluminium body.