Maria Sharapova has announced she failed a drugs test at the Australian Open.

The 28-year-old Russian made the shocking revelation at a pre-arranged press conference in Los Angeles, on Monday.

Sharapova, who has played in only one tournament this year, losing to Serena Williams in the quarter-finals of the Australian Open, said she received a letter from the ITF informing her of the failed test for meldonium - a substance which has been on the banned list since January 1, 2016.

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Sharapova, who took "full responsibility" for the failed test, said she has been taking the drug legally since the age of 16, but did not realise it had subsequently been banned.

"I received a latter from the ITF that I failed a drugs test at the Australian Open," said Sharapova. "I take full responsibility for it.

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#WTA CEO Steve Simon's statement in response to @MariaSharapova's announcement. pic.twitter.com/DhasT9Mrpo

— WTA (@WTA) March 7, 2016

"For the past 10 years I have been given a medicine called mildronate by my family doctor and a few days ago after I received the ITF letter I found out that it also has another name of meldonium which I did not know.

"It is very important for you to understand that for 10 years this medicine was not on WADA's banned list and I had legally been taking the medicine for the past 10 years.

"But on January 1st the rules had changed and meldonium became a prohibited substance which I had not known."