Former Ukrainian politician Andriy Portnov, who worked as a senior aide to pro-Russian former President Viktor Yanukovych, has been shot dead just outside the Spanish capital Madrid, a Spanish national police source told CNN.

Spanish authorities say an adviser to former Ukrainian President Viktor Yanukovych was killed outside the American School of Madrid.

Police said witnesses had reported Andriy Portnov was shot "several times" in the head and body by more than one gunman when he was getting into a black Mercedes