"At this point, [we have] not seen [Beijing] take the step of providing weapons [to Moscow]. We are watching closely," Sullivan told "This Week" co-anchor Martha Raddatz.
"We know they haven't taken it off the table. We are sending a clear message, as are our European allies, that this would be a real mistake because those weapons would be used to bombard cities and kill civilians. China should want no part of that."
Sullivan admitted that it was difficult to say whether China is "backing on [or] backing off" of the decision to send weapons. "What I can say is, so far, we have not seen them do it," he told the ABC anchor. (Related: China offers to join forces with Russia to 'defend national interests' as Xi's Moscow visit confirmed.)
Days earlier on Feb. 24, President Joe Biden told David Muir of ABC's "World News Tonight" that the U.S. would definitely respond the moment Beijing sends military aid to Moscow.
Biden continued: "I don't anticipate. We haven't seen it yet, but I don't anticipate a major initiative on the part of China providing weaponry to Russia."
The president recounted a conversation he had with Chinese paramount leader Xi Jinping, in which he warned the head of the communist country about the economic impact of helping Russia. Biden mentioned to Xi the 600 American companies that left Russia after the latter launched a special military operation.
"And I said: 'If you are engaged in the same kind of brutality by supporting the brutalities going on, you may face the same consequence.'"
Meanwhile, Beijing has defended its relationship with Moscow as one "built on the basis of non-alliance, non-confrontation and non-targeting of third countries.
According to the national security advisor, Biden has ruled out sending F-16 fighter jets to Ukraine "for now" – despite repeated requests from Ukrainian President Volodymyr Zelensky. Calling the matter "a question for later," Sullivan reiterated that Washington's current focus is to help Ukrainians "retake territory on the ground" in the beleaguered country's south and east.
"Every phase of this war, the president has tried to make sure that the Ukrainian military gets what they need. In the first phase as they were defending Kyiv that was javelin anti-tank weapons and Stinger anti-air systems. And that worked; it helped Ukraine defend Kyiv," he said.
"In the second phase, it was heavy artillery to help them hold against the Russians pushing in eastern Ukraine. In this [third] phase, the critical element is ground maneuver capability. That means tanks, armored personnel carriers [and] infantry fighting vehicles. So what the president is saying is he's focused on these capabilities."
Upon further pressing by Raddatz about the possibility of fighter jets being sent to Ukraine, Sullivan responded: "We will cross the bridge of future phases of this war when they come."
A week earlier, Secretary of State Antony Blinken told Raddatz another reason why Biden refuses to supply Kyiv with jets when he appeared on "This Week." According to Blinken, the F-16s would require training and maintenance – which is not the current priority in the ongoing conflict.
"From our perspective, the most important thing that we can do is make sure that we maintain focus on what is the highest priority. Honestly … the highest priority right now is to move as rapidly as possible to build up their capacity to de-occupy those portions of Ukraine that are still being occupied brutally and bloodily by Russian forces," Blinken said.
"That will be the central focus of the Ukrainians as well as of our support for the Ukrainians in the weeks and months ahead."
Visit WWIII.news for more stories about the ongoing Russia-Ukraine war.
Watch Clayton Morris of Redacted News as he talks about President Joe Biden's package of 31 M1 Abrams tanks to Ukraine.
This video is from the In Search Of Truth channel on Brighteon.com.