UPDATE 1-SAfrica mine unions snub new gold sector wage offer

* Unions say offer still too low

* Next round of talks last chance to avert strike

(Adds details, Solidarity union)

JOHANNESBURG, July 14 (Reuters) - Workers in South Africa's gold sector rejected the latest offer for a pay raise of between 8 percent and 10 percent and vowed to soon escalate the dispute, the National Union of Mineworkers (NUM) said on Tuesday.

Three South African unions are holding talks with gold producers under the guidance of a mediator after failing to agree on wage increases. The unions have warned they could strike if negotiations fail.

"NUM has this morning rejected the Chamber of Mines' offer of between 8 and 10 percent from gold employers and will escalate the dispute on July 21," NUM spokesman Lesiba Seshoka said.

The union -- South Africa's biggest mineworkers body -- received the improved offer on Monday but said the increase might not be enough to avert a strike.