Sam Neill has joined the cast of 'Thor: Ragnarok'.

Sam Neill

Sam Neill

The 'Jurassic Park' actor spent "a couple of days" shooting a role in the upcoming Marvel Comics adventure - which will see Chris Hemsworth reprise his role as the titular character alongside the likes of Mark Ruffalo, Cate Blanchett and Jeff Goldblum - but he insisted he had been sworn to secrecy about his part.

He told ShortList magazine: "I'm not really allowed to say this and I can't tell you what it is... I did a couple of days on 'Thor' just before I came over here. If I say anything else, Marvel's secret agents -- and they are lethal -- will come and get me and probably my children, as well."

Shooting on the movie, which will be directed by Taika Waititi, began in Australia in July.

The film will see The Hulk (Ruffalo) make an appearance to help his Avengers teammate with a huge threat looming over Asgard.

Natalie Portman is reportedly not returning to the series as Thor's previous love interest Dr. Jane Foster, but Tom Hiddleston, who plays Loki, will return for what may be his last time "out of the gate" as the villain.

Hiddleston previously said: "Thor 3' will be cool because I've not done it for four years. I love working with Chris. This will be my last time out of the gate."

And the latest 'Thor' instalment will bring a "new style of humour".

Speaking previously, director Taika said: "My strength in this is bringing my style of humour, which is probably a very different style of humour. They've had good jokes in them before, but I think where I come from is maybe a fresher style. It could just shake the entire thing up a bit."

'Thor: Ragnarok' is scheduled to hit cinemas in November 2017.