Ukrainian President Volodymyr Zelensky on Friday warned in an interview with AFP that Russia's offensive in the Kharkiv region this month may only be a "first wave" and Russian troops could aim for the city of Kharkiv.

Zelensky said the situation in the region, where Russia has seized several border villages, was "controlled" but "not stabilised" after Ukraine sent reinforcements.

The president also said Russian troops had penetrated between five to 10 kilometres along the northeastern border before being stopped by Ukrainian troops.

Russia's offensive "could consist in several waves. There was the first wave" in the Kharkiv region, he said.

"I won't say it's a great success" for Russia, he said.

But he added: "We have to be sober and understand that they are going deeper into our territory. Not vice versa. And that's still their advantage."

Russia began its offensive on May 10, forcing thousands of people to flee their homes as Russian troops pounded villages along the border and made their biggest territorial gains in Ukraine since the end of 2022.

Speaking about it for the first time during a visit to China on Friday, Russian President Vladimir Putin said the offensive was a response to Ukraine shelling border regions of Russia.

"I said publicly that if this continues, we will be forced to create a security zone," he said.

When asked about whether Russia planned to capture the city of Kharkiv, which has over a million inhabitants, Putin said: "As for Kharkiv, there are no such plans as of today.

But Zelensky said that Russian forces "want to attack" the city although they realise it would be "very difficult".

"They understand that we have forces that will fight for a long time," he said.

Zelensky also said Ukraine and its Western allies should not show weakness and called for the deployment of two Patriot batteries to defend the skies over the Kharkiv region and show resilience against Moscow.

"They are like a beast... If they feel a weakness somewhere in this direction, they will press on," he said.