"We see that China is investing heavily in new, modern weapons, including new missiles," Stoltenberg said on German ZDF public television, according to the German translation.

"And half of their missiles would violate the INF treaty if China were a signatory," he said, referring to the 1987 nuclear weapons control accord that US President Donald Trump last month threatened to quit.

Stoltenberg added: "We support expanding this treaty so that China is also bound by it."

Trump warned last month the US could pull out of the Intermediate Range Nuclear Forces accord, a pillar of Cold War disarmament, in response to Russia's deployment of a missile system Washington says breaches the accord.

Russian President Vladimir Putin has warned that abandoning the treaty could lead to a new arms race, and vowed to respond in kind if the US deployed any new missiles on European soil.

Stoltenberg said Tuesday that "NATO does not want a new arms race, but we are very worried about the new Russian missiles... they are mobile, they are nuclear-capable and they can reach cities in Europe like Berlin".

"So we call on Russia to make sure they stick to the INF treaty... this treaty is now in danger."