North Korea would face tougher sanctions if it carries out yet another nuclear test, including greater restrictions on its labor exports, the top State Department official on Asian affairs was quoted as saying Tuesday.

Assistant Secretary of State Daniel Russel made the remark to Reuters amid growing indications and concern that the North could conduct what would be its fifth nuclear test, just a few months after the fourth test that sparked global condemnations and toughest-ever U.N. sanctions on Pyongyang.

"Like a regimen of medicine, the dosage can be upped when the effects fall short of what's required," Russel was quoted as saying.

The official said that fresh sanctions can be imposed by the U.N. Security Council, by the United States unilaterally, or by a group of like-minded states from the European Union and Southeast Asia, along with the U.S., according to the report.

Russel also said that the U.S., South Korea and Japan could also take "defense-related measures" in response to a new nuclear test. He didn't elaborate what the measures would be, but they are believed to be things like bolstering missile defense systems and increasing strategic defense assets in the region.

"As the threat grows, then our defensive capabilities need to adjust as well," he was quoted as saying.

In response to the North's nuclear test in January and its long-range rocket launch the following month, South Korea and the U.S. decided to launch official discussions on the potential deployment of the THAAD missile defense system to the South.

The U.S. also sent a B-52 nuclear bomber from Guam to fly over South Korea in a show of force designed to send a warning to North Korea and reassure its ally of Washington's security commitment in the wake of the North's nuclear test.

The two allies also conducted their annual military exercises on a larger scale than before. (Yonhap)