The directors of the latest Avengers film have pleaded with fans not to reveal plot details after some footage and images reportedly leaked online.

In their letter to "the greatest fans in the world", the Russos said they had worked "tirelessly" to deliver "a surprising and emotionally powerful conclusion to the Infinity Saga".

"Remember, Thanos still demands your silence," they continued - a reference to the film's main villain, a genocidal warlord played by Josh Brolin.