R&B star Erykah Badu is under fire from human rights activists after performing for Swaziland's controversial King Mswati Iii.

The singer serenaded Mswati for his 46th birthday as a favour for a friend last Thursday (26Apr14), but was unaware of the leader's reputation, which includes criticisms of his polygamy and lavish lifestyle in the poor nation, as well as allegations of torture and human rights abuses.

Human Rights Foundation's Alex Gladstein slams Badu in a statement which reads: "She owes us all an explanation. The king is a kleptocrat who lives in the lap of obscene luxury while most of his countrymen toil in abject poverty for less than $2 (£1.18) a day."

Badu defended her impromptu performance in an interview with the Dallas Morning News in Texas, and explained her friend, American jeweller Jacob Arabo, was organising the birthday party for Mswati and needed a last-minute replacement for a performer who had unexpectedly pulled out of the event.

Badu was recording her album in South Africa at the time, and hopped on a helicopter to attend the celebration in the Mavuso Centre in Manzini, where she sang Happy Birthday then handed the King a gift from Arabo.

She also took to Twitter.com on Tuesday (29Apr14) to defend her actions and wrote, "I was not paid by the King. I had no idea of the political climate. All the people were smiling when I sang. I was smiling. We All felt good in that moment."