Beyonce announces she is pregnant and expecting twins

American pop star Beyonce is pregnant and expecting twins.

In a post on her Instagram account, the singer wrote: "We have been blessed two times over.

"We are incredibly grateful that our family will be growing by two, and we thank you for your well wishes."

Beyonce and Jay Z are already parents to Blue Ivy, who was born in 2012.

The couple, who married in 2008, routinely make the listings of the most powerful people in the entertainment world.

In 2013 the singer told ABC News that she "would like more children".

She added: "I think my daughter needs some company. I definitely love being a big sister."

Beyonce set a record in December for earning Grammy Award nominations for her diverse album 'Lemonade' - appearing in the rock, pop, R&B and rap categories.

She is due to perform at the Grammy ceremony on Sunday, February 12.