Hungary cultivates closer ties with Russia than other European Union states, and is seen as the key potential opponent to a decision due in December on whether to open EU accession talks with Ukraine, which would require the unanimous backing of the bloc's 27 members.

With great pomp, Viktor Orban and Putin held talks in China on Tuesday. Broadcast on Russian television, Orban told Putin that he had never wanted to oppose Moscow and is trying to salvage bilateral contacts.

"It was very, very unpleasant to see that," Kallas, one of Ukraine's staunchest defenders, told Reuters in an interview in Paris. "How can you shake a criminal's hand, who has waged the war of aggression, especially coming from a country that has a history like Hungary has?"

The International Criminal Court (ICC) issued an arrest warrant against Putin in March, accusing him of the war crime of illegal deportation of children from Ukraine.

"It is not so distant past what happened in Hungary, what the Russians did there," Kallas said.

The 1956 Hungarian Uprising was crushed by Soviet tanks and troops. At least 2,600 Hungarians and 600 Soviet troops were killed in the fighting.

After holding talks with French President Emmanuel Macron, Kallas said Ukraine's allies should not get distracted by other conflicts and redouble their efforts to show they are in it for the long haul.

The immediate priority, she said, was to "increase the cost of aggression" by adding new sanctions, urgently tackling the circumvention of existing measures and to find ways for Kyiv to use frozen assets.

"The conflict is not frozen, it is a war of attrition," she said. "It's also understandable that Russia is thinking that they can endure the pain much longer than we are enduring the pain and he's (Putin) really playing on this."

When asked whether next year's U.S. elections could be a game changer, she said Washington's allies would have to deal with whoever was in power, but that so far in her talks with Democrats and Republicans there was still a strong voice for supporting Ukraine.

With war raging between Israel and Hamas, the immediate attention has turned away from Ukraine and other flashpoints in the region such as the fallout after Azerbaijan's military operation in Nagorno-Karabakh and rising tensions in the Western Balkans.

"The war in Middle East, of course, takes the oxygen away from all the other discussions. This is the reality, but it doesn't mean that we should lose our interest in these areas," Kallas said.