The U.S. State Department said the Quad security alliance has not developed procedures for cooperation with outside partners, likely indicating there is no intent to accept any further members.

A spokesperson gave this response to Voice of America, which asked the department about South Korean President-elect Yoon Suk Yeol's campaign pledge to join the Quad, which consists of the U.S., Australia, India and Japan.

According to VOA on Saturday, the State Department said the South Korea-U.S. alliance, along with strong economic ties and close friendship of their people, is the linchpin for peace, security, and prosperity in the Indo-Pacific. 

It said the U.S. is committed to the defense of South Korea and looks forward to working with President-elect Yoon to deepen cooperation on key global challenges, including climate change, the pandemic and supply chain issues. 

The U.S.-led Quad was formed to exercise checks on China's influence in the Indo-Pacific.