Workers at Southern Railway are to stage a fresh 48-hour strike in the long-running row over the role of guards.

The Rail, Maritime and Transport (RMT) union announced its members will walk out on September 7 and 8, causing fresh travel chaos for beleaguered passengers.

Southern's services have been disrupted for months because of industrial action and staff shortages, blamed by the company on high levels of sickness absence.

Workers have taken several bouts of industrial action in recent weeks and mounted picket lines at stations across Southern's network.

Commuters and other passengers have also staged demonstrations to protest at the level of services.

Changes to the role of guards were imposed from Sunday, transferring responsibility for closing doors to drivers.

RMT general secretary Mick Cash said: "This action has been forced on us by the arrogance and inaction of Govia Thameslink and the Government, who have made it clear they have no interest in resolving this dispute or in tackling the daily chaos on Southern.

"Instead they have begun the process of bulldozing through the drive towards wholesale driver only operation (DOO) without agreement and without any concern for the impact on safety, security and disability access.

"Our fight is with the company and the Government who have dragged this franchise into total meltdown.

"We share the anger and frustration of passengers and we cannot sit back while jobs and safety are compromised on these dangerously-overcrowded trains.

"It is disgraceful that neither the company nor the Government are prepared to engage and are looking to bully through the extension of DOO and the attack on the guards from last Sunday regardless. They should wake up and get round the table now as an urgent priority."

Southern passenger service director Alex Foulds said: "Passengers and staff will once again be appalled by the RMT's decision to hold yet another strike. We are moving forward with our plans for the benefit of customers after nine months of fruitless attempts to reach an agreement.

"This action is unnecessary, unjustified and futile. We have guaranteed all our onboard staff a job until the end of the franchise, as valued members of our future operation, with no reduction in salary.

"And claims that safety is at risk are just untrue. The independent rail safety body has said so, and nearly half our trains run without conductors already."

A spokesman for the Rail Delivery Group, representing train operators and Network Rail, said: "This further strike action will cause misery for thousands of passengers.

"We know there are no risks to jobs or pay and drivers have been closing train doors safely elsewhere on the railway for the last three decades.

"The rail industry must modernise to deliver the better service today's customers expect and deserve.

"This dispute is about changes that would mean a better on-board service for passengers and less disruption when problems hit the railway."

Rail minister Paul Maynard said: "This will be disappointing news for passengers who should not be made to suffer any further disruption from strikes or other unjustified action.

"I hope all parties can find a way to work together to deliver a modern railway, with the additional capacity and improved performance passengers want."