To build out a more elaborate personal assistant for the Messenger users, Facebook has acquired an artificial intelligence (AI) startup Ozlo that specialises in understanding text-based conversations.

The four-year-old startup claims that its virtual assistants can understand and provide answers to questions which do not have simple "yes" or "no" answers.

"By joining a team (Facebook) that shares our values and our vision, we will be able to continue to work on building experiences powered by artificial intelligence and machine learning," a post on Ozlo's website read.

Ozlo has raised $14 million from a number of investors, including Greylock.

The startup has 30 employees, majority of which will be joining Messenger in Facebook's offices in either Menlo Park, California or Seattle, Washington.

"They're just going to be working with [Messenger] to continue their work with artificial intelligence and machine learning," a report in Recode on Monday quoted a Facebook spokesperson as saying.

However, there are no details so far about the financial terms of the deal.

Earlier this year, Messenger's product head Stan Chudnovsky said Facebook was focused on text-based AI because voice conversations like that of Apple or Google required an extra step.

"Until we nail [text] we don't want to go into a world where we teach people what we cannot do well. Otherwise we're going to be in the world where people very quickly realise certain things that we don't do well yet and then they may not give us another try," Chudnovsky said.