Washington, Mar 30 (IANS): Former US President Barack Obama's Kenyan step-grandmother and the family's matriarch, Sarah Obama, has passed away aged 99 years old.

Taking to Twitter on Monday, the former President said: "My family and I are mourning the loss of our beloved grandmother, Sarah Ogwel Onyango Obama, affectionately known to many as 'Mama Sarah' but known to us as 'Dani' or Granny.

"We will miss her dearly, but we'll celebrate with gratitude her long and remarkable life."

Sarah Obama, who passed away early Monday morning, had been admitted with undisclosed illness at Jaramogi Oginga Odinga teaching and referral hospital located in the western Kenyan county of Kisumu.

Born in 1922 in a village on the shores of Lake Victoria, Sarah Obama was the third wife of Hussein Onyango Obama, the former President's grandfather.

Sarah rose to global fame when her step-grandson was elected the first African-American US President, and her modest homestead in western Kenyan county of Siaya has been a prized destination for local and foreign tourists.

The Obama matriarch, who will be buried on Tuesday in line with Islamic traditions, was eulogised by Kenyan leaders as a patriot and gallant fighter for the rights of women and girls.

In a condolence message, Kenyan President Uhuru Kenyatta said: "She was a loving and celebrated philanthropist who graciously shared the little she had with the less fortunate in her community."