The US Air Force has started a review after failing to provide information to authorities that would've stopped the Texas shooter from legally buying firearms.

Devin Kelley killed 26 people when he opened fire at a church in Sutherland Springs on Sunday.

Five years earlier, as an airman, he was convicted of domestic assault against his wife and stepson.

If reported, the conviction should have prevented him from buying firearms - but officials now say it appears the information was not entered into a database.

An Air Force spokesperson said the organisation "has launched a review of how the service handled the criminal records of former Airman Devin P. Kelley following his 2012 domestic violence conviction".

The US Department of Defence has also said it will carry out an investigation "to determine whether information about Kelley's conviction was properly entered into the National Criminal Information Center database".