"It is clear that North Korea is learning from those tests and improving their capabilities, with the ultimate goal of reaching the US homeland," he said in a statement.

The senator called for actions to curb the North's threats.

"The time for rhetoric is over. It is time for concerted action," he said, calling the situation on the Korean Peninsula "the most unstable point since the armistice" that ended the 1950-53 Korean War.

"The administration must immediately ramp up the sanctions track, especially against the Chinese that are enabling North Korea's nuclear program. I do not believe we are putting requisite pressure against China that is necessary to stop Pyongyang, and I'll continue to urge the administration to do so," he said. (Yonhap)