Former Ukrainian president stationed in Kyiv says 'we are not giving up' as Russian forces inch closer

• Former Ukrainian President Petro Poroshenko called Russia's Vladimir Putin a "war criminal."
• During a CNN appearance, Poroshenko said that despite dwindling resources, Ukraine is "not giving up."

The former president of Ukraine referred to Russian President Vladimir Putin as a "war criminal" amid the ongoing Russian war in Ukraine.

"Please don't trust Putin. Please don't trust Russia. I think Putin is a war criminal," former president Petro Poroshenko told CNN from the frontlines of Kyiv. "He is a mad person."

Russian forces have continued to press towards the Ukrainian capital since their invasion began on February 24. In over two weeks of fighting, there have been some 1,546 confirmed Ukrainian casualties, The United Nations said Friday.

"But we have less and less ammunition," Poroshenko said. "We are not giving up."

He added: "I am absolutely confident that we will fight in every single house, every single street, and every single quarter in Kyiv, in Kharkiv ... in all of the cities would be the hell for the Russian soldiers and would be at the end of the day the hell for Putin."

"He underestimate unity of Ukraine and that he cannot blow up, cannot break our unity," the former president added of Putin.

Poroshenko also made an appeal to Western countries for additional resources, including food, ammunition, military jets, antitank missiles, and anti-aircraft missiles.

Western countries have slapped sanctions on Russia, targeting Putin and his inner circle of oligarchs. Last week, the US House of Representatives approved a spending package that included nearly $14 billion in military and humanitarian aid for Ukraine.

The Department of Defense also recently rejected Poland's proposal to send its Russian-made MiG-29 warplanes to Ukraine via a US airbase. Poland's ambassador to the US later said he understood the rejection, adding that sending warplanes could be seen as an escalation of the conflict.

On Saturday, Russia warned the United States that any convoys carrying weapons into Ukraine will be considered "legitimate targets."

On CNN, Poroshenko dismissed false claims by the Russian government that the US is harboring bioweapons in Ukraine.

"Me, as a president of Ukraine, can guarantee no chemical, no bacteriological weapons; Ukraine don't have, don't have it before and not planning to have it in the future. This is definitely confirmed. This is classical, very important example of the Russian propaganda," Poroshenko said.

The Kremlin has organized a pervasive propaganda campaign about the war, criminalizing sharing information about the invasion domestically and threatening dissenters with arrest and prison time.