Restkit - Wait for completion and stop all operation if something fails

Question

I have a batch of requests that I build as follow:

for(int i = 0; i < count; i++)

{
     RKObjectRequestOperation *operation = [objectManager appropriateObjectRequestOperationWithObject:nil                                           method:RKRequestMethodPOST                                                                       path:@"sync.json"                                                                          parameters: nil];
        [operation setCompletionBlockWithSuccess:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult)
        {

        }
                                         failure:^(RKObjectRequestOperation *operation, NSError *error) {

        }];
        [objectManager enqueueObjectRequestOperation:operation];
        [operation waitUntilFinished];
}

The code is supposed to stop and wait to every single operation before going on. How can I stop or rather remove all queued operation if something goes wrong? Maybe by using cancelAllObjectRequestOperationsWithMethod?

[EDIT]

In Restkit 0.20 maybe is better to use objectManager postObject:reqObj...