"What they have is a giant hammer. They could hurt North Korea by shutting down all economic relations and trade but that would likely generate a large number of refugees, something the Chinese aren't interested in."

The U.N. has already passed two resolutions aimed at preventing North Korea from launching ballistic missile technology and suspending all activities related to its missile program.

North Korea claims the rocket tests will enable it to launch a satellite but many nations consider the launches a cover for testing ballistic missiles.

The U.S. tried to tighten sanctions against North Korea in the wake of April's failed launch by targeting banks, businesses and government entities that are violating the resolutions, but China vetoed all but three of the 40 entities the U.S. had suggested should be added to the sanction list.

The other forum for engaging Pyongyang are the "six-party talks" between South Korea, Japan, China, the U.S. and Russia. Plans to resume the talks after Kim Jong Un took power in December, following the death of his father, were scuppered after North Korea's failed missile launch in April.