Facebook's rumoured new smartphone may have been leaked on Twitter just days before it is expected to be unveiled. See also: Where to watch Android Facebook Phone event live.

An image of what appears to be a device called the 'HTC First' has been published by Twitter account @evleaks.

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The image shows no HTC branding on the phone. The device appears to have Android's traditional three capacitive buttons below the screen, but the home button indicator is a hollow circle. See also: How to get Facebook Home on your Android smartphone.

Facebook has scheduled a press event later this week where the company is widely expected to unveil a smartphone built entirely around the social network.

The image comes just a day after US blog Android Police published details of what appeared to be a leaked version of a Facebook OS.

The HTC First is expected to be a mid-range device. It is likely to come with a dual-core processor and a 5-megapixel camera and will run the Android 4.1.2 Jelly Bean operating system.