Ukrainian President Volodymyr Zelensky told CNN that Ukraine is not willing to give up territory in the eastern part of the country to end the war with Russia, and Ukraine's military is prepared to fight Moscow's military in the Donbas region in a battle he says could influence the course of the entire war.

Zelensky said in an exclusive interview Friday with CNN's Jake Tapper from the office of the president in Kyiv that his country has no guarantee that Russia wouldn't try again to seize Kyiv if it is able to capture Donbas.

"This is why it is very important for us to not allow them, to stand our ground, because this battle ... it can influence the course of the whole war," Zelensky said.

"Because I don't trust the Russian military and Russian leadership," he continued. "That is why we understand that the fact that we fought them off and they left, and they were running away from Kyiv -- from the north, from Chernihiv and from that direction -- it doesn't mean if they are able to capture Donbas, they won't come further towards Kyiv."

Zelensky's interview with CNN Friday, more than seven weeks into Russian President Vladimir Putin's attack on Ukraine, comes as Ukraine's military has seen successes resisting Russia's offensive that have come as a surprise to US intelligence -- and a Kremlin that had planned for a quick and decisive victory.

Asked by Tapper if Ukraine would be victorious in the conflict, Zelensky said, "Yes, of course, and will."

At the same time, however, Ukraine has suffered horrific civilian casualties across the country amid the fighting. Zelensky told CNN that the world should be prepared for the possibility that Putin would use a tactical nuclear weapon because he does not value Ukrainian lives. Zelensky spoke in both Ukrainian and English about the horrors his country has witnessed and the urgent help his military still needs to be equipped to fend off the coming Russian offensive in the east and southern parts of Ukraine.

US President Joe Biden said last week that the civilian killings being committed by Russian forces appeared to be genocide.

"I have the same opinion as President Biden," Zelensky said. "Look what happened in Bucha. It's clear that is not even a war, it's a genocide. They just killed people. Not soldiers, people. They just shot people in the streets. People were riding bicycles, taking the bus or just walking down the street. There were corpses lining the streets."

French President Emmanuel Macron, who has engaged Putin diplomatically, said in response to Biden's comments on genocide that he didn't think it was constructive to raise the rhetoric. Zelensky said he spoke to Macron this past week and wants him to visit Ukraine to see the atrocities firsthand.

"I think he wants to take some steps to ensure that Russia engages in dialogue. I just told him that I want him to understand that this is not war, but nothing other than genocide," Zelensky said. "I invited him to come when he will have the opportunity. He'll come and see, and I am sure he will understand."

Zelensky said he also wants Biden to come to Ukraine. The US President suggested last week that he wanted to go, though he said US officials are still "in discussions" on whether a high-level US official will visit Ukraine.

"I think he will," Zelensky said of Biden when asked if there were any plans for the US President to visit. "I mean, his decision, of course. And as well, the safety situation depends -- I mean that -- but I think he's the leader of the United States, and that's why he should come here to see."

Asked about a video released last week showing a Ukrainian woman finding the body of her son in a well, Zelensky said, "This is the most horrifying thing I have seen in my life."

He grew emotional talking about the death that the war has caused in Ukraine, saying it is "a great pain for me" to see the lives lost. Zelensky, who lost family in the Holocaust, was asked what he thought about politicians around the world saying "never again" on International Holocaust Remembrance Day, given what's happening in his country.

"I don't believe the world," he said, speaking in English. "We don't believe the words. After the escalation of Russia, we don't believe our neighbors. We don't believe all of this."

"The only belief there is belief in ourselves, in our people, belief in our Armed Forces, and the belief that countries are going to support us not just with their words but with their actions," Zelensky continued in Ukrainian. "And that's it. Never again. Really, everybody is talking about this and yet, as you can see, not everyone has got the guts."

More help needed

Zelensky said the $800 million in additional funding Biden approved last week to go to Ukraine for new and more advanced weapons was helpful -- but more was still needed.

"Of course, we need more. But I am happy that he is helping us now," Zelensky said. "I feel that right now we are having a cleaner dialogue. It's been a dialogue that's had some twists and turns. And not just talk. It's been very, very difficult because there aren't many countries that have really helped us."

Zelensky said the most important factor was speed to get the weapons needed into the hands of Ukrainian forces. He dismissed some concerns the US and other countries have raised that Ukraine's soldiers are not trained to use some of the weapons the country is asking for.

"There are people that are offering solutions, but it seems they are just self-serving. So it's precisely not up to us," Zelensky said. "We are prepared to use any type of equipment, but it needs to be delivered very quickly. And we have the ability to learn how to use new equipment. But it needs to come fast."

Zelensky said that he's prepared to engage with Russia diplomatically to try to end the war but that Russia's attacks on Ukrainians make it harder to do.

"As I said before, what's the price of all this? It's people. The many people who have been killed. And who ends up paying for all of this? It's Ukraine. Just us," Zelensky said. "So for us, this is a really great cost. If there is an opportunity to speak, we'll speak. But to speak only under a Russian ultimatum? It's then a question about attitude towards us, not about whether the dialogue is 'good' or 'bad.' It's impossible."

Acknowledging that he still has a target on his back from the Kremlin as the war rages on, Zelensky was asked how he would want to be remembered.

"A human being that loved life to the fullest," he responded. "And loved his family and loved his motherland. Definitely not a hero. I want people to take me as I am. A regular human."