Planned strikes by London Underground workers in a row over an all-night Tube service have been suspended.
Members of the Rail, Maritime and Transport union, Unite and the Transport Salaried Staffs Association were due to stage two 24-hour walkouts from Tuesday and Thursday evenings, which would have caused travel chaos in the capital.
The three unions announced a suspension of the action, although the RMT set two new strike dates for next month unless a deal is achieved.
The union said it remained in dispute and will strike on September 8 and 10 if there is an attempt to impose the new service.
Unite said it had suspended the strikes as a "gesture of goodwill" to allow further talks to be held.
Unions are in dispute over pay and shifts for the new service, which is due to start at weekends from September 12.
The drivers' union Aslef had already decided not to strike this week.
The four unions involved in the long-running row have held two 24-hour strikes in the last month which closed the Tube network completely, causing travel misery for millions of commuters and tourists.
RMT general secretary Mick Cash said: "Our negotiators have been able to make enough significant progress in talks at Acas over pay, jobs and night Tube to allow us to suspend this week's strike dates.
"We have still not reached a final agreement and as a result we are putting on additional strike action next month. In the meantime, the talks process will continue.
"I want to pay tribute to the union members who have remained united and rock solid throughout this dispute. It is their determination which forced LU to begin talking seriously and which has enabled us to make the progress that we have so far.
"Our dispute is not with the working class of London and RMT is not opposed to night Tube providing it is introduced properly with safe and robust staffing arrangements which recognise the substantial extra pressures that this expansion will inevitably create."
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.
"We will continue to approach talks with London Underground in a positive manner. We trust that London Underground management seize this opportunity to reach a deal that fully addresses our members' concerns and secures a successful future for night running on the Tube."
TSSA leader Manuel Cortes said: "I am extremely pleased to say that our negotiating team has made sufficient progress to suspend this week's planned strike action on the Tube.
"However, we are not out of the woods yet. A number of issues need to be resolved before our dispute is finally settled. We will therefore announce future strike dates in due course although we remain hopeful that further talks will soon result in a negotiated settlement."
Labour's London Assembly transport spokeswoman Val Shawcross said Mayor Boris Johnson should now speak with the unions and help draw the dispute to a close.
"Londoners will remember that Boris Johnson was quick to claim the credit when announcing the night Tube, but the second things got tricky he was nowhere to be seen.
"There are now less than three weeks to go until the night Tube is due to start. The mayor needs to be straight with Londoners if that date is no longer viable, as further uncertainty could well mean businesses who are expecting the night Tube to be running for the Rugby World Cup are left out of pocket."
Mr Johnson said: "I welcome the unions' decision to suspend an unnecessary strike that would have caused huge inconvenience to Londoners and businesses.
"I would urge the unions to continue with positive discussions that will help to deliver a night Tube service that will bring huge benefits to our city."
Acas said: "We are pleased that following extensive conciliation talks at Acas, this week's Tube strike has been called off."
Nick Brown, LU's managing director, said: "It is good news for London that the strike has been suspended. We will now continue to work with the unions so that we can resolve this dispute and get on with delivering for our customers, businesses and London."
LU repeated it was "operationally ready" to start the new service on time.
Transport Secretary Patrick McLoughlin said: "I welcome the unions' decision to suspend these unnecessary strikes. They would have caused massive disruption for hardworking Londoners and visitors to the capital, and significantly affected business. We will deliver the modern, reliable Underground system London deserves, and I hope all parties will work with us to achieve it."