WASHINGTON - The United States has called on nuclear weapon States to exercise restraint regarding the use and testing of their nuclear capabilities, while stressing the need for building confidence-building measures.

“We continue to urge all States with nuclear weapons to exercise restraint regarding nuclear and missile capability testing and use, and we encourage efforts to promote confidence building and stability with respect to those capabilities," State Department Spokesman John Kirby told reporters at the daily Press briefing on Monday.

Kirby was responding to a question by an Indian journalist about Pakistan’s test-firing of its first nuclear-capable submarine cruise missile.

“We have seen reports of this missile launch – submarine-launched missile,” he said without specially referring to Pakistan's missile launch Pakistan on Monday successfully test-fired its first Submarine-Launched Cruise Missile capable of carrying a nuclear warhead up to 450km from an undisclosed location in the Indian Ocean, giving the country a "credible" second-strike capability.

The missile, Babur-3, was fired from an underwater, mobile platform and hit its target with precise accuracy, the Inter Services Public Relations said in a statement.“