'Alien: Romulus' director Fede Álvarez is still "trying to find a story that is worthy of everyone's time" as he continues working a sequel to his sci-fi horror.

Álvarez's entry into the 'Alien' franchise proved to be a box office hit in the summer and so 20th Century Studios have approached him for a follow-up.

The 46-year-old filmmaker is up for making a sequel but he will only commit to another movie focused on the Xenomorph.

Speaking with io9, he said: "[It's] not until we find something that we go 'OK, that is a movie worth making' that we really embark on it.

"So that's the process we are in right now, trying to find a story that is worthy of everyone's time and is worthy of the title. Otherwise, you never want to fall into the mistake of making [a sequel] just because the first one is a big hit."

'Alien: Romulus' - which starred Cailee Spaeny, David Jonsson and Isabela Merced - is set after Sir Ridley Scott's original 'Alien' from 1979, and follows a group of space colonizers who find themselves the prey of a dreaded Xenomorph as they explore an abandoned space station.

As well as Álvarez, both Spaeny and Jonsson were confirmed to reprise their respective roles of Rain and Andy in the sequel.

In an interview with The Hollywood Reporter last month, 20th Century Studios boss Steve Asbel said: "We're working on a sequel idea now. We haven't quite closed our deal with Fede, but we are going to, and he has an idea that we're working on.

"The two survivors, Rain and Andy, played by Cailee Spaeny and David Jonsson, were real highlights of the film. And so I always think of it like, 'Wow, where do people want to see them go next?'

"We know there's going to be aliens. We know there's going to be great horror set pieces. But I fell in love with both of them and I want to see what their story is."