WASHINGTON: Expressing concern over India's recent ballistic missile launch, the US has said such actions could potentially "increase" the risk to nuclear security and have an impact on regional security."We're concerned by any nuclear and missile developments that could potentially increase the risk to nuclear security risk or lower the threshold for nuclear use," the State Department Spokesman, Mark Toner, told reporters."So we continue to urge all states with nuclear weapons to exercise restraint regarding their missile and nuclear capabilities," Toner said when asked about recent ballistic missile test by India.He said the State Department official had shared its concerns with New Delhi."We are concerned," he reiterated yesterday when asked if the US was concerned about India's ballistic missile programme."We are concerned about those kind of actions what they do for regional security," he said.While his answer was general in nature, a senior State Department official pointed out that it included India and the spokesperson's response was against India-specific question."Yes," Toner said when asked if the US had raised its concerns with India on its ballistic missile programme.A day earlier he had refrained from going into specifics of America's bilateral conversations with India on this issue."I don't want to get into specifics of our bilateral conversations with India, but we've long encouraged efforts to promote confidence building, stability, and discourage any actions that might destabilise the region," he had said.India successfully launched an indigenously-developed, nuclear capable K-4 ballistic missile from a submerged platform in the Bay of Bengal recently.