Talks to avert Tube strikes over concerns about safety issues have broken down.

The Rail Maritime and Transport Union (RMT) and Transport Salaried Staffs Association (TSSA) claim talks came to an end after London Underground went back on its promise not to use agency staff at stations.

The unions, which represent 7,500 station staff and drivers, also say safety standards are at risk under plans to close up to 40 ticket offices and reduce opening hours.

They also have concerns about staff working alone and plans to introduce "mobile supervisors" at stations.

RMT general secretary Bob Crow said: "When LUL took guards away they said there was no need to worry because there would be enough station staff to keep things safe, but the concept of mobile station supervisors drives a coach and horses through the safety regime and the rule book, and passengers should be worried.

"What happens when there's a fire, someone under a train or any one of dozens of possible emergencies and the person in charge is at the wrong station or even stuck between stations?"

TSSA balloted on strike action end Tuesday and the RMT is currently serving notice of its ballot.

TSSA senior regional organiser John Page said: "This dispute boils down to LUL wanting to put casual staff on stations in place of properly trained Tube staff."