Hopes of averting fresh strikes by thousands of London Underground workers were hit today when union leaders were accused of refusing to attend new peace talks.

LU wrote to the Rail Maritime and Transport union (RMT) and the Transport Salaried Staffs Association (TSSA), calling on them to return to negotiations today to break the deadlocked dispute ahead of a second planned strike next month.

The two sides spent six hours at conciliation service Acas on Wednesday 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.

The company said today that the unions had refused to return to Acas, adding that they were continuing to demand that LU should withdraw plans to axe 800 jobs before talks could progress.

Howard Collins, LU's chief operating officer, said: "We met with the leaderships of the TSSA and RMT unions at Acas for six hours on Wednesday and were, once again, faced with the demand that we withdraw our plans in their entirety before talks can progress.

"We cannot agree to this demand - the simple fact is that our customers' needs have changed, with some ticket offices now selling fewer than 10 tickets per hour, and so London Underground needs to change.

"Despite their claims that this dispute is about safety, the union leaderships have not even tried to make the case or present any evidence to us to support that argument.

"Our plans have no impact on safety standards and we have also given a cast-iron guarantee that these plans involve no compulsory redundancies or loss of earnings. We have assured the unions 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 were hoping that the union leaderships would come to Acas today to try to avoid further disruption to Londoners. Unfortunately they have refused, showing that, for all their words, they were not serious about averting another strike. 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, call off this pointless industrial action and stop threatening Londoners with disruption."

Manuel Cortes, assistant general secretary of the TSSA, said: "LU's proposals do not go far enough for us to resume talks 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."

TSSA leader Gerry Doherty said London Mayor Boris Johnson was "playing politics" with the travelling public in the capital, adding: "It is his orders that 800 ticket jobs must go regardless that is preventing positive talks going ahead.

"He wants to set us up as the bad guys for his big Tory conference speech in Birmingham in two weeks time. That is why he is happy to see the October 3 walkout go ahead.

"We are prepared to discuss cost savings but we will not accept the 800 figure before sitting down to discuss those savings. He seems to be prepared to climb over the three million people who use the Tube as part of his long term plan to get to Downing Street."