Tensorflow: Different results with the same random seed

I'm running a reinforcement learning program in a gym environment(BipedalWalker-v2) implemented in tensorflow. I've set the environment seed and the random seed of tensorflow manually as follows

env = gym.make('BipedalWalker-v2')
env.seed(0)

tf.set_random_seed(42)

However, I get different results every time I run my program (without changing any code). Why are the results not consistent and what should I do if I want to obtain the same result?