Russell Simmons has congratulated Beyonce Knowles on her pregnancy.

Although the 31-year-old singer hasn't confirmed speculation that she and husband Jay-Z are set to welcome a new addition to their family, the hip-hop mogul - who is a close friend of the couple - tweeted his congratulations.

He tweeted: ''Congratulations Jay-Z & Beyonce.''

Beyonce recently admitted she would love to give her 16-month-old daughter Blue Ivy a sibling, because she enjoyed such a close relationship with her younger sister Solange Knowles, 26, when they were growing up.

She said: ''I would like more children. I think my daughter needs some company. I definitely love being a big sister.''

When pressed on when she may have another child, she added: ''At some point, when it's supposed to happen.''

The superstar - who is currently on her 'Mrs. Carter Show World Tour' - also revealed she doesn't use her full range of vocal talents when she sings nursery rhymes to 16-month-old Blue Ivy and saves her ''Beyonce voice'' for the stage.

She explained: ''I do [sing to Blue Ivy] but I have a mommy voice. I keep my Beyonce voice for the stage and I have my simple mommy voice.

''I remember hearing a story about Celine Dion and she was like, 'When I sing, I don't know if it was her son, cried.' And that's so interesting she has the most beautiful voice in the world and she's like, 'He hates it.' So I say well maybe I'll just give a little simple nursery rhyme voice to my daughter.''