Demi Lovato is backing a campaign to support equal marriage rights.

The 21-year-old singer-and-actress - who is an avid supporter of equality for the LGBT community - has asked Americans to ''stand up for what's right'' and end discrimination of same-sex couples.

In an e-mail sent out by the 'Americans for Marriage Equality' campaign, Demi wrote: ''My generation knows that it's wrong to tell two people in love they can't get married, simply because of who they love.

''We've got to stand up for what's right and let our voices be heard if we want to put an end to marriage discrimination. The America I know and love values everyone, and that includes the LGBT community.''

The 'Warrior' singer also recorded a video to support the campaign, in which she said allowing same sex couples to marry would ''strengthen the institution of marriage''.

Demi said: ''I believe that love comes in all different shapes, sizes and colours. So whether you're LGBT or straight, your love is valid, beautiful and an incredible gift.

''So let's protect them and strengthen the institution of marriage by allowing loving, caring and committed same sex couples to legally marry.''

In America, 31 states still do not allow couples of the same sex to marry.

Demi - whose new track 'Really Don't Care' was filmed at Los Angeles Pride - asked the public to back the campaign via an online petition.