China’s Xi Jinping urges restraint from Donald Trump amid fears of North Korea nuclear test

Satellite imagery analysed by 38 North, a Washington-based monitoring project, found some activity at North Korea's Punggye-ri nuclear test site last week.

However, the group said it was unclear whether the site was in a "tactical pause" before another test or was carrying out normal operations.

Tensions escalated further on Sunday when North Korea detained a US citizen as he attempted to leave the country.

President Trump has sought China’s help to rein in North Korea’s military programme, but has also vowed to act unilaterally if it failed to do so.

China, the North’s only diplomatic ally and trading partner, banned imports of coal from its neighbour in mid February after tough UN sanctions were imposed on Pyongyang.

Chinese media has raised the possibility that Beijing could choke the country of crude oil, a potentially devastating move for Kim's regime.