London Underground urged union leaders today to resume peace talks aimed at averting fresh strikes by Tube workers in a row over job losses.

The company wrote to the Rail Maritime and Transport union and the Transport Salaried Staffs Association, calling on them to return to negotiations to break the deadlocked dispute ahead of a second planned strike next month.

The two sides spent six hours at the conciliation service Acas yesterday but the meeting ended without agreement, with union leaders warning that a 24-hour walkout was likely to go ahead from October 3 and further stoppages were planned for November.

The unions staged a 24-hour strike earlier this month in protest against plans to cut 800 jobs, which caused disruption to Tube services.

Howard Collins, LU's chief operating officer, said the unions continued to demand that the company withdraws its staffing plans before talks can progress.

"With some ticket offices now selling fewer than 10 tickets per hour London Underground needs to change, and we cannot agree to this demand.

"Despite their claims that this dispute is about safety, the unions' leaderships have not even tried to make any case to us that these proposals impact upon safety standards.

"We have assured the unions' leaderships that our plans have no impact on safety standards and have given a cast-iron guarantee that these plans involve no compulsory redundancies or loss of earnings. We have assured them again that every station that has a ticket office now will have one in future, and all stations will be staffed at all times.

"We remain ready and willing to discuss any aspect of our proposals, including any specific safety concerns, and we hope the leaderships of the TSSA and RMT will return to talks at Acas tomorrow, call off this pointless industrial action and stop threatening Londoners with disruption."

It seemed unlikely that the unions will attend any talks tomorrow, although officials are in contact with Acas.

Manuel Cortes, assistant general secretary of the TSSA, said: "LU's proposals do not go far enough for us to resume talks tomorrow but we are now in contact with Acas to try and resolve some of the more difficult issues between us.

"It would certainly help if LU stopped talking nonsense about ticket offices selling fewer than 10 tickets an hour when there are only half a dozen in that position in a network with over 400 booking offices."

RMT leader Bob Crow said: "The ball is firmly in LU's court now. Our contact through Acas is ongoing and it is down to LU to come back with a positive response that gives us a solid basis to recommence talks.

"Simply banging the drum about ticket office closures that the Mayor himself has publicly opposed gets us nowhere. This dispute is about safety, safe staffing levels and the quality of customer service and those issues must be addressed seriously."