Commuters in London face a further period of heightened transport misery after tube workers announced five days of strikes. Members of the RMT union will strike for 48 hours from the evening of Monday 28 April and again for 72 hours from the following Monday, 5 May.

The strike announcement comes after eight weeks of talks between unions and London Underground management over plans to close station ticket offices and cut about 900 jobs. The talks were prolonged by the death in March of the RMT leader, Bob Crow, who had led the opposition to mayor Boris Johnson's proposals for "modernisation" of the tube, but called off a second set of strikes in favour of talks at Acas.

However, the TSSA union, which took action alongside the RMT in February, has chosen to continue holding talks with tube bosses next week, along with Aslef and Unite. That means there will be significantly fewer employees on strike than during the previous two days of industrial action, when Transport for London bosses said the majority of regular Oyster card users still made journeys on tubes, buses or trains.

The RMT blamed "management intransigence" and the introduction of additional measures during the consultation process for the decision to strike. The union also believes further cuts to jobs and pay are planned.

The RMT's acting general secretary, Mick Cash, said: "The assurances that were given at the time RMT suspended the original action for a proper evaluation of the cuts plans have been ripped up and thrown back in our faces.

"An opportunity to resolve this dispute through eight weeks of talks hosted by ACAS has not only been missed, it has been sabotaged. As a result, RMT has no option but to put on further strike action in the expectation that the management will now halt these dangerous cuts plans and engage in meaningful and serious talks on the future of a tube network running at full tilt, with further demands in the pipeline, which needs more staff and not less to operate safely."

London Underground said it had constructive talks with the unions and denied that staff would lose pay. Phil Hufton, London Underground's chief operating officer, urged the RMT to call off the strike and remain in talks. He said: "Rather than our staff being stuck behind glass screens in under-utilised ticket offices, they will be at ticket machines, gate lines and platforms.

"Over the past eight weeks, we have met with our trades union colleagues on over 40 occasions, listening to their concerns and making significant changes as a result. I've committed to looking at ways to ensure that no one will lose pay and no supervisor will have to apply for their own job. There will be no compulsory redundancies and all requests for voluntary redundancy will be honoured.

"However, the RMT leadership has rejected these changes and has not put forward any credible alternative proposals."

TfL said that less than 3% of journeys involve a journey to the ticket office - a claim that the RMT said it had already exposed as "a bare-faced lie".

A TfL spokesman said the proposals meant every tube station would be staffed by a customer service supervisor.

Negotiations were overshadowed in March by Bob Crow's sudden death after he had led the RMT for 12 years and been Britain's most recognisable union leader. An impending leadership election in the RMT may also affect the eventual settlement.

The union is to hold a rally in Trafalgar Square in honour of Crow, as well as the late Labour politician Tony Benn, on 1 May, just after the first 48-hour strike.