"There are clear signs, and the Chinese side has shared with us some of the signs they're seeing," he said. "We see certain signs of our own through intel and other sources we have that it is creating some stress within North Korea's economy and with some of their citizens, potentially even within some of their military."

Tillerson did not elaborate.

The UN Security Council adopted sanctions resolutions after Pyongyang's long-range missile tests in July and its sixth and most powerful nuclear test in September.

They are designed to cut off revenue for the communist regime and stop its development of nuclear missiles that could reach as far as the US mainland. (Yonhap)