The wife of the Russian opposition activist, Vladimir Kara-Murza, has told the BBC's Sarah Rainsford that she believes her husband was poisoned.

Mr Kara-Murza, a fierce critic of Vladimir Putin, is currently on life support in a Moscow hospital after his wife says he suffered multiple organ failure for the second time in two years.

The hospital will not comment publicly on his condition, but Evgenia Kara-Murza says she has sent samples to clinics abroad for toxicology tests.