Rail union RMT has announced two additional days of strikes as a dispute over driver-only trains at ScotRail continues.

Union bosses said workers would stage 24-hour walkouts on Sunday, July 24 and Sunday, July 31 after discussions failed to make progress.

The union is opposed to the extension of driver-only and driver-controlled services during the lifetime of the current Abellio ScotRail franchise on safety grounds.

It says it has not received assurances it has sought on the issue, and that the "core issue at the heart of the dispute" had not been addressed.

A series of strikes in June and July have already caused disruption for passengers.

In a statement, they said: "RMT has repeatedly attempted to engage in serious talks through ACAS but progress has been blocked as the company have tried to pick and choose issues and divide and rule the workforce.

RMT general secretary Mick Cash said: "The entire trade union movement stands shoulder to shoulder with the ScotRail staff fighting for the basic principles of rail safety who once again showed their resilience and determination over the weekend in the latest phase of industrial action.

"Despite this series of rock-solid strikes it is extraordinary that Abellio/Scotrail continue to ignore the strength of feeling amongst their staff over the extension of DOO. That disgraceful and cavalier approach to jobs and safety on Scotland's railways now leaves us with no choice but to put on additional strike dates."

Mr Cash added that removing guards from Scotrail services was a "lethal gamble with basic rail safety".

ScotRail has insisted that the solution to the dispute could only be solved by talks rather than industrial action.

In a statement on its website following the announcement of the latest round of strikes, the firm said: "We think this strike is totally unnecessary. The RMT say we're planning on having driver-only trains. We are not.

"We will always schedule a second person on trains to serve our customers. They say it's about safety. It is not. Today, 59% of our customers travel on a train where the doors are safely opened and closed by the driver.

"The body in charge of regulating safety on the UK rail network - the ORR - say this is a safe way of working."

It said that around three-quarters of its services would run on July 24 and July 31, however passengers are urged to check timetables.