"I don't believe that he will use these weapons," Zelensky told the TV station of Germany's Bild newspaper, referring to nuclear arms. "I don't believe that the world will allow him to use these weapons."

The Ukrainian leader warned against giving in to Putin's threats.

"Tomorrow, Putin can say -- as well as Ukraine, we want part of Poland, otherwise we will use atomic weapons. We cannot make these compromises," he said.

The Russian president's decision to order a partial mobilisation was because of the low morale among his forces, said Zelensky.

"He needs an army of millions... he sees that a large part of those (troops) who come to us, just run away," he said.

Putin "wants to drown Ukraine in blood, also the blood of his own soldiers", Zelensky said.

Putin announced early Wednesday the mobilisation, as Ukraine mounts a lightning counter-offensive and seizes back swathes of territory, and also hinted that Moscow could use atomic arms over the conflict.

Annexation referendums set to be held in Russian-occupied areas of Ukraine were "sham referendums", Zelensky said, adding 90 percent of states would not recognise them.

The Ukrainian leader said his nation's forces would push on with their military campaign and "free our territory".

He reiterated that Kyiv wants Germany to send battle tanks to aid Ukraine in the fight against Russia, heaping fresh pressure on Chancellor Olaf Scholz's government.

While Berlin has sent some armaments to Ukraine, they have so far refused to transfer the tanks that Kyiv is urgently appealing for.

"Give us these weapons," Zelensky said. "Battle tanks mean that more people's lives can be saved."

He criticised the German government's position that it does not want to "go it alone", as no other ally has transferred Western-made battle tanks to Ukraine.

"You are an independent state... don't say 'First the US, then Poland, and so on'."

Zelensky also said he believes Putin has "already lost the war".

"From the first day of the invasion of Ukraine's territory, he had lost this war. No one will forgive him."