Soldiers of the People's Liberation Army of China at Tiananmen Square during a military parade in 2015 marking the 70th anniversary of the end of World War II. Reuters Amid a productive phone call between President Donald Trump and Chinese President Xi Jinping, Chinese state-run media reported that 150,000 Chinese troops went to North Korea's border.

Both China and the US have pushed back on the claims of troops massing, however.

International observers fear that North Korea may conduct another nuclear test this weekend on the anniversary of the founding of Kim Jong Un's regime, but the US has broadcast loud and clear that nuclear posturing in the Korean peninsula will no longer be tolerated.

In March, Business Insider talked to Sim Tack, a North Korea expert at Stratfor, a geopolitical-analysis firm, who speculated how Chinese forces could stop North Korea's nuclear program without firing a shot.

Tack predicted China would "definitely react to and try to prevent" a US strike on North Korea. The US increasingly has touted military strikes as an option against the Kim regime, even going as far as positioning an aircraft carrier off Korea's coast.

"The overt presence of Chinese forces would dissuade the US from going into that territory because they would run the risk of inviting that larger conflict themselves," Tack said.

Chinese forces in North Korea would "be in a position to force a coup or force Kim's hand" to disarm, Tack said.

Ultimately, China, North Korea's biggest backer, would attempt "to make sure North Korea still exists and serves Chinese interests while it stops acting as a massive bullseye to the US," he added.

North Korean leader Kim Jong Un at the Korean People's Army Tank Crews' Competition 2017. Reuters/KCNA KCNA

In this way, China could preserve its buffer state from falling to Western influence, prevent a US military strike on its borders, and even prevent a nuclear war.

Besides its possible troop buildup, China also seems willing to apply pressure to the Kim regime in other ways. Last week, Beijing ordered its customs authorities to reject coal imports from North Korea — a big hit to the regime's wallet, since coal makes up about 40% of its total exports.