Activities spotted in North Korea could be preparations for a nuclear test explosion, a South Korean news report said Monday.

Increased movement of personnel and vehicles around the site of Punggye-ri in the north-east of the country was similar to the activity preceding North Korea’s previous test, the JoongAng Ilbo reported, citing unnamed high-ranking government officials in Seoul.

There was also speculation that the North might test-fire a missile, the presidential office said.

North Korea deployed two mid-range rockets on mobile launchers somewhere on the east coast last week, Seoul officials said Friday.

Tensions have risen on the peninsula since North Korea’s third nuclear test on February 12, which led to tightened sanctions against the isolated regime.

The Communist country has issued several threats, including of a nuclear strike against the United States, and declared the 1953 cease-fire with the South invalid.

On Tuesday, Pyongyang said it was restarting its nuclear facility at Yongbyon, which would allow it to resume production of weapons-grade nuclear material.

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