* Labour strife, soaring costs, low prices cloud talks
* AMCU says Chamber of Mines trying to divide workers (Adds comments from AMCU in sixth, seventh paragraphs)
JOHANNESBURG, July 29 (Reuters) - South Africa's Chamber of Mines has declared a dispute with labour group AMCU in gold negotiations, a move aimed at placing wage talks for the entire sector before a government-affiliated mediator, it said on Monday.
"AMCU has rejected the gold producers' revised offer of a 5 percent increase in wages and benefits. The producers have indicated that they cannot accede to AMCU's demands, in respect of which AMCU has not moved at all in respect of its demands," the chamber said in a statement on behalf of gold producers.
The next step in the labour talks, billed as the most difficult since the end of apartheid in 1994, is for all parties to take the dispute to the Commission for Conciliation, Mediation and Arbitration (CCMA) for mediation.
Last week, three separate unions in the talks with the gold mining firms represented by the Chamber of Mines declared an official dispute, saying two weeks of talks had stalled and needed outside help.
The Association of Mineworkers and Construction Workers Union (AMCU), a militant union new to collective bargaining in the sector, did not join the other groups.
AMCU President Joseph Mathunjwa criticised the gold firms and chamber for trying to force it into mediation with the other unions and said his labour group had been planning to hold a round of wage talks with the mining houses on Aug. 1.
"The Chamber of Mines from the onset never recognised AMCU as a bargaining agent. The Chamber of Mines is an architect of dividing workers," he told Reuters.
The wage talks are set against a backdrop of increased union militancy that has coincided with soaring costs and falling prices for gold.
Bullion producers are offering a wage increase of 5 percent, slightly below South Africa's 6 percent inflation rate and well short of the 60 to 100 percent pay hike demanded by workers.
South Africa's labour laws allow for wage disputes to be referred to an outside mediator. If that fails, employees are allowed to go on a legal strike.
Last week, the NUM, Solidarity and UASA unions, which will collectively approach a mediator, represent 73.6 percent of the 120,000 mineworkers employed by gold producers in pay negotiations, declared the official wage dispute. (Editing by David Evans)