The US has voiced concern over China's test launch of a nuclear-capable missile and assured its allies of being steadfast in its defence commitments to them. The US also urged China to engage in meaningful arms control discussions and notify the intercontinental-range ballistic missile and space launches in line with the commitments made by the five permanent members of the UN Security Council -- China being one of them. China on Monday successfully test-fired a long-range strategic missile with a dummy warhead from one of its nuclear-powered submarines in the Pacific Ocean.