Here's Mr. Stoltenberg's statement in a video (1 min)
The head of Nato has told the BBC that China should face consequences for supporting Russia's war in Ukraine, if it does not change its ways.
Jens Stoltenberg said Beijing was "trying to get it both ways" by supporting Russia's war effort, while also trying to maintain relationships with European allies.
"This cannot work in the long run," Mr Stoltenberg told BBC News during a visit to Washington.
In the wide ranging interview, Mr Stoltenberg also addressed nuclear weapons and defence spending.
His comments come as Russia shows no sign of easing its war against Ukraine.
A peace summit held in Switzerland at the weekend saw dozens of nations commit to supporting Kyiv, but Russia called it a waste of time and said it would only agree to peace talks if Ukraine essentially surrendered.
When pressed on what Nato members might do about China's support of Russia, Mr Stoltenberg said there was an "ongoing conversation" about possible sanctions.
He said China was "sharing a lot of technologies, [like] micro-electronics, which are key for Russia to build missiles, weapons they use against Ukraine".
He added that "at some stage, we should consider some kind of economic cost if China doesn't change their behaviour".
Beijing is already under some sanctions for its support of Russia - last month, the US announced restrictions that would target about 20 firms based in China and Hong Kong.
China has defended its business with Moscow, saying it is not selling lethal arms and "prudently handles the export of dual-use items in accordance with laws and regulations".
Mr Stoltenberg's visit to Washington came as the Kremlin confirmed that Vladimir Putin will travel to North Korea on Tuesday.
It follows his visit to China last month.
Russia has become increasingly isolated on the world stage since it launched its full-scale war with Ukraine in 2022. Mr Putin has repeatedly said that the West's balance of power is shifting, and he has worked to strengthen ties with like-minded leaders.
"Russia right now is aligning more and more with authoritarian leaders," Mr Stoltenberg told the BBC, listing Iran, Beijing and North Korea.
He said that the North has sent artillery shells to Russia, and in return Russia had given advanced technology for North Korea's missile and nuclear programmes.
"So North Korea is helping Russia to conduct a war of aggression against Ukraine."
Speaking ahead of a meeting with US President Joe Biden, the Nato chief also announced that more than 20 nations are expected to meet a defence spending target of 2% this year - more than any other year since it was pledged in 2014.
"This is good for Europe and good for America, especially since much of this extra money is spent here in the United States," he said.
Mr Stoltenberg also addressed comments that he made to the Telegraph on Sunday which indicated that Nato may be considering increasing the number of deployable warheads as a deterrent against growing threats from Russia and China.
The comments were criticised as "nothing but another escalation of tension" by Kremlin spokesman Dmitry Peskov.
But Mr Stoltenberg said they were a "general message" that Nato is a nuclear alliance, and that any attack on a Nato member will "trigger a response from the whole alliance".
"The purpose of Nato is not to fight the war, the purpose of that is to prevent the war," he said.