Dream Hampton, a writer and activist who worked with Jay Z on his 2010 memoir "Decoded," made the revelations in a series of messages on Twitter that were deleted but were posted by the hip-hop magazine Complex.

"When we needed money for bail for Baltimore protesters, I... hit Jay up, as I had for Ferguson (and he) wired tens of thousands" of dollars within minutes, read one tweet.

She also tweeted that Jay Z and his pop superstar wife Beyonce wrote a "huge check" to support the burgeoning "Black Lives Matter" movement aimed at stopping police brutality.

Protests spread last year after a white police officer shot dead African American teenager Michael Brown in the St. Louis suburb of Ferguson.