WASHINGTON, June 15 (Reuters) - The United States targeted North Korea's missile development in fresh sanctions, issuing the punitive action after South Korea earlier on Thursday said its neighbor fired two short-range missiles.

The South Korean military said North Korea fired two short-range missiles off its east coast on Thursday, less than an hour after Pyongyang warned of an "inevitable" response to military drills staged earlier in the day by South Korean and U.S. troops.

The U.S. Treasury Department in a statement said it imposed sanctions on two North Korean nationals it accused of being involved in the procurement of equipment and materials that support the country's ballistic missile program.

"The United States is committed to targeting the regime’s illicit procurement networks that feed its weapons programs," the Treasury's Under Secretary for Terrorism and Financial Intelligence, Brian Nelson, said in the statement.

Thursday's action targeted a Beijing-based representative for the Second Academy of Natural Sciences, which Washington said is a national-level organization responsible for research and development for North Korea's advanced weapons systems. His wife, who Washington said is assigned to the North Korean embassy in China, was hit with sanctions as well.

The Treasury in the statement said North Korea continues to use a network of representatives abroad, including in China and Iran, to illicitly import components necessary for its weapons of mass destruction and ballistic missile programs.

North Korea's ballistic missile and nuclear weapons programs are banned by United Nations Security Council resolutions that have sanctioned the country.

Diplomatic efforts to reduce tensions or persuade Pyongyang to abandon its nuclear arsenal have been stalled.