Yoko Ono has thanked Lady GaGa for covering John Lennon's hit 'Imagine' at a Human Rights Campaign dinner in Washington DC.

The singer included the song in her set as a tribute to gay college student Matthew Shepard, who was murdered in 1998.

Altering some of the lyrics, Lady GaGa sang: "Imagine there's no heaven/ It's easy if you try. No hell below us/ And only Matthew in the sky."

Shepard's murder, which witnesses claimed was due to his sexuality, brought international attention to the issue of hate crime legislation.

In a message on Twitter, Ono, the widow of the former Beatle, wrote: “Dear Lady GaGa, Thank you for singing 'Imagine'.

“Hearing that made me choke up. You are so beautiful! In Sisterhood and love, Yoko.”

GaGa took to the stage in the US capital after President Barack Obama, who pledged his “unwavering” commitment to end a ban on gay people from serving in the American military.

He also joked at the end of his speech about his position on the line-up.

"It's privilege to be here tonight to open for Lady Gaga. ... I've made it,” he said.

On Sunday, Lady GaGa joined thousands of protesters on the National Equality March, which led calls for equality across America.

(by Jason Gregory)