Talks aimed at averting a strike by London Underground workers have ended without agreement and a 48-hour walkout will go ahead from 9pm.
Leaders of the Rail, Maritime and Transport (RMT) union held a last-ditch meeting with London Underground (LU) at the offices of the conciliation service Acas to resolve a row over ticket office closures.
But the talks lasted only a couple of hours and broke up with no sign of a breakthrough.
The union said it had put forward proposals which it believed could have led to the industrial action being suspended.
London mayor Boris Johnson attacked the union and described the strike as "pointless".
RMT acting general secretary Mick Cash said: "London Underground have dug themselves into an entrenched position and have refused to move one inch from their stance of closing every ticket office, in breach of the agreement reached previously through Acas which enabled us to suspend the previous round of action.
"Despite the spin from LU, nothing that they are proposing is about 'modernisation'. The current plans, closing every ticket office and axing nearly a thousand safety-critical jobs, is solely about massive austerity cuts driven centrally by David Cameron and his Government and implemented by mayor Boris Johnson.
"RMT could have recommended the suspension of this strike action if LU had responded positively to our proposal to halt the implementation of these savage cuts, stopping the dire impact they would have the length and breadth of London Underground."
An Acas spokesman said: "The meeting between RMT and London Underground this morning has now finished. Our services remain available to the parties and we will continue to maintain close contact with the parties."
A three-day strike is planned for next week.
Mr Johnson said: "I urge the RMT to call off this pointless strike and get back round the table with London Underground and the three other unions who've chosen not to strike.
"It seems the RMT leadership is set against modernisation and has no fresh ideas of its own.
"More than 600 people have asked for voluntary redundancy and yet, without consulting any of their own members, the RMT is suddenly insisting that London Underground halt this process.
"Despite dozens of meetings over several months, the RMT chose only on Friday to make fresh demands. It seems they are more interested in fighting over the leadership of the RMT than the interests of their members.
"Commuters and businesses will suffer because a few narrow-minded union barons are currently flexing their muscles in a fight for the leadership of a union where just 30% of members support a strike."
LU warned there will be disruption to services from this evening, with Tubes starting later and finishing earlier than normal tomorrow and Thursday.
Buses and other transport services will be busier than normal.
Tube services are unlikely to serve the area around Arsenal, where a Premier League football match is being held this evening.
Phil Hufton, London Underground's chief operating officer, said: "Our plans will radically improve the service we offer Tube customers in future. The whole Tube station will effectively become a personalised customer service centre, with more staff visible and available to help customers buy the right ticket, plan their journeys and get assistance.
"Over the past eight weeks, we have met with trades unions on more than 40 separate occasions.
"We have listened to their concerns and made changes as a result. We've provided guarantees that not a single member of staff will be forced to leave LU, that no supervisors must 'apply for their own job' and we are seeking ways to ensure that no member of staff sees their pay cut as a result of these changes.
"Given these commitments and guarantees, Londoners will rightly be asking why the RMT is threatening five days of strikes.
"All it will achieve is disruption to Londoners and a loss of pay for all those staff who take part. My message to the RMT leadership is it's not too late to call off this unnecessary strike and continue to work with us to help shape the future of the Tube.
"We will be working hard to keep London moving and open for business."
Mike Brown, managing director of London Underground, said: "The RMT leadership appear to remain implacably opposed to the modernisation of the Tube that will radically improve customer service and help us keep fares down.
"For example, at our busiest stations, there will be nearly a third more staff visible and available to provide, on a permanent basis, the face-to-face customer service we offered during the London 2012 Games. Visitors to London and people with disabilities will be better looked after than ever before.
"Safety and security will never be compromised. Safety is not controlled from ticket offices but by station supervisors and dedicated control rooms. This will continue.
"Fairness to our staff is also guaranteed. There will be no compulsory redundancies, there is a job for all staff wanting to remain with us and no one will lose pay as a result of change.
"We have also made significant changes to our original proposals after listening to staff and unions in over 40 meetings, including agreeing that supervisors will not need to 'reapply for their jobs'.
"However, the RMT leadership continues to say 'no' to everything. And they also appear in the context of these changes to be opposed to giving our staff the option of voluntary redundancy. They are simply making it up as they go along.
"Only the RMT leadership know the real motivations behind their actions, but it is infuriating that London's commuters and businesses are the ones who are being forced to pay the price with five days of utterly pointless and disruptive strikes. They should call it off.
"We have asked all the trade unions to continue talking to us this week and we hope that they continue to do so."