Unions representing London's Underground staff on Monday called off two 24-hour strikes planned for this week, which threatened more chaos for commuters already hit by walkouts over plans for night services.

Three unions -- the Rail, Maritime and Transport union, Unite and the Transport Salaried Staffs' Association -- cancelled the strikes due for Wednesday and Thursday as a "gesture of goodwill".

However, the RMT announced new strikes for September 8 and 10 if a deal is not reached over pay and conditions governing the night Tube.

Staff have already staged two strikes -- one in July and one this month -- forcing millions of Londoners to walk, cycle or take packed buses to and from work.

Unions are locked in a months-long dispute with management over London Mayor Boris Johnson's plans to run a 24-hour Tube service on Fridays and Saturdays from September 12 on certain lines.

The Tube handles four million journeys every day, meaning many buses and overground trains become packed during the strikes.

Unite regional officer Hugh Roberts said: "There are still some remaining sticking points, but we feel sufficient progress has been made to suspend industrial action as an act of goodwill."