Thousands of workers on London's underground rail network have called off a 72-hour strike, unions said on Thursday, after negotiations with management alleviated concerns over safety and staffing.

The strike, which was due to start on Sunday, would have affected millions of commuters at a crunch time for London Mayor Ken Livingstone ahead of mayoral elections on May 1.

Transport unions the RMT and TSSA - who represent more than 7,500 workers on the underground - said management had dropped plans to close or reduce ticket office opening times and had pledged to provide full safety training to all staff .

"The paramount importance of Tube safety for both staff and passengers has been recognised in this deal and our members will no longer face the threat of a two-tier workforce," TSSA General Secretary Gerry Doherty said in a statement.

"We now must work together to improve industrial relations throughout London Underground to make sure we do not find ourselves facing a fiasco like this in the future."