Ukrainian President Volodymyr Zelenskyy has pleaded with U.S. leaders and NATO to impose a no-fly zone over his country as it continues warring with Russia, setting off a debate about the consequences such a move would have. 

"If there were a no-fly zone, and we had to enforce it, that would mean U.S. planes flying concurrently with Russian ones. And you'd run the risk of U.S. planes downing Russians or vice versa," Dan Hoffman, a Fox News contributor and former CIA station chief in Moscow, told Fox News Digital. 

A no-fly zone bans aircraft from a specific area and is sometimes used over government buildings for security reasons. The zones have also been imposed during times of conflict to prevent military aircraft from attacking the area. 

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Hoffman told Fox News Digital that going back to the Cold War, U.S. strategy has dictated "no direct, kinetic engagement with the Soviet Union or with Russia."

"That means our soldiers aren't raising their firearms to go shoot them in the face and vice versa," he said.

Instead, the U.S. has fought proxy wars with Russia since the end of World War II, including currently in Ukraine. A no-fly zone, however, could change that and put U.S. soldiers in direct conflict with Russians. 

Ukraine's President Volodymyr Zelenskyy

Ukraine's President Volodymyr Zelenskyy holds a press conference on Russia's military operation in Ukraine on Feb. 25, 2022, in Kyiv.  (Presidency of Ukraine/Handout/Anadolu Agency via Getty Images)

Zelenskyy held a Zoom call with more than 280 U.S. lawmakers Saturday and pleaded for "urgent" military support and humanitarian aid, including "control of the skies" to combat Russia. He also called on NATO and President Biden last week to impose a no-fly zone over "significant parts" of the country. 

"We repeat every day: ‘Close the sky over Ukraine!'" Zelenskyy said in a video posted to Twitter Sunday, accompanied by English subtitles. 

But his appeals have hit a brick wall. 

NATO and the White House have denied imposing the no-fly zone, while some U.S. leaders have described such a move as coming with disastrous consequences. 

"The only way to implement a no-fly zone is to send NATO fighter planes into Ukrainian airspace, and then impose that no-fly zone by shooting down Russian planes," NATO Secretary-General Jens Stoltenberg said. "We understand the desperation, but we also believe that if we did that, we would end up with something that could end in a full-fledged war in Europe." 

NATO Secretary General Jens Stoltenberg

NATO Secretary General Jens Stoltenberg speaks during a media conference after a meeting of the NATO-Ukraine Commission at NATO headquarters in Brussels, Tuesday, Feb. 22, 2022.  (AP Photo/Olivier Matthys)

A no-fly zone risks a direct military conflict with Russia. It has the potential of escalating to a third world war, pitting nuclear power countries such as the U.S., France and the U.K. against fellow nuclear power Russia

A recent Reuters/Ipsos poll found that 74% of Americans across the political spectrum support a no-fly zone. But some U.S. leaders say the issue is far more complicated than just prohibiting aircraft over Ukraine. 

"If people understand what it means, it means World War III. It means starting World War III," Republican Florida Sen. Marco Rubio said Saturday on ABC's "This Week." "It's not some rule you pass that everybody has to oblige by. It's the willingness to shoot down the aircrafts of the Russian Federation, which is basically the beginning of World War III."

Democrats have also sounded the alarm on imposing a no-fly zone, including Connecticut Sen. Chris Murphy. 

"I think we need to be clear that we are not going to go to war with Russia, that would be the beginning of WWIII, and it would drag all of Europe into a much broader war," Murphy said on "Fox News Sunday."

Zelenskyy addressed such concerns Monday and said that Russian aircraft bombing his country, including schools, "need to be shot down" to "preserve lives."

"I'm sure that the brave American soldiers who would be shooting it down knowing that it is flying towards the students — I'm sure that they had no doubt in doing so," he told ABC News. 

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Some U.S. lawmakers, such as Democratic Sen. Joe Manchin, however, have signaled that the no-fly zone option should remain on the table, while retired NATO supreme commander U.S. Air Force Gen. Philip Breedlove said that a humanitarian no-fly zone could allow for relief trains to get into the country and for the wounded to be cared for. 

Hoffman told Fox News Digital that he understands why Zelenskyy is asking for the no-fly zone as it rings the alarm bells that the Ukraine leader is saying "help me or else I'm dead." 

Hoffman said that instead, the U.S. could offer assistance in the form of halting Russian oil and gas from being imported and getting Ukraine air-defense systems and anti-tank missiles. 

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Russia invaded Ukraine on Feb. 24, and the battles have continued raging in various ports and major cities. Zelenskyy addressed European leaders Friday and said that if Ukraine is victorious, "this will be the victory for the whole democratic world." 

"If we will fall, you will fall, so please don't be silent, do not turn the blind on eye on this," he added.