Singer Ariana Grande has spoken publicly for the first time about the death of her former boyfriend Mac Miller, writing on social media that he was "the kindest, sweetest soul with demons he never deserved".

Paramedics found Miller, a 26-year-old platinum hip-hop star whose real name was Malcolm McCormick, unresponsive in his Los Angeles home on September 7 and declared him dead soon after.

An autopsy was performed, but no cause of death has yet been announced.

In a message on her official Instagram account, 25-year-old Grande said she "adored" Miller from the day she met him when she was 19.

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"You were my dearest friend for so long," she wrote alongside a video of Miller laughing.

"I'm so sorry I couldn't fix or take your pain away. I really wanted to.

"I'm so mad, I'm so sad, I don't know what to do."

Social media users blamed death on break-up

Following Miller's death last week, Grande posted a black and white photo of Miller without a caption.

She then disabled comments on the account after people began to blame the rapper's death on their break-up.

The two had dated for two years, but the relationship ended earlier this year. Grande is now engaged to Saturday Night Live star Pete Davidson.

Miller had discussed his use of drugs, particularly the misuse of prescription cough syrup, in media interviews and rap lyrics.

He first gained a following at age 18 with his mixtape K.I.D.S. in 2010, and early in his career was known for party-style songs with videos that went viral.

After his 2011 debut Blue Side Park was released by an independent label and topped the charts, Miller turned to jazz and funk influences on later albums.

Those releases often received praise from critics, but did not perform as well commercially as his first album.

AP/Reuters