Voicing Groot is very challenging: Vin Diesel

Action star Vin Diesel says voicing Groot in Guardians of the Galaxy is very challenging as the limited vocabulary makes it hard to get emotion across.

The 49-year-old actor's character in the Marvel Comics movie franchise is a tree-like humanoid named Groot who can only say "I am Groot", reported Contactmusic.

"It's very challenging because you're limited to three words. There's a secret script that I get where it has all of Groot's lines. But all that I can say is: 'I am Groot'," Diesel said.

The actor said he is set for an even bigger challenge in the upcoming second installment of the franchise, as Groot, who was seen sacrificing himself at the end of the 2014 movie and re-growing into Baby Groot, will need a much higher voice to encapsulate his small size. "I have a feeling they'll do a combination of things. I mean, I do it super high-pitched".