Ukrainian President Volodymyr Zelensky won diplomatic backing from Europe and the Nato alliance on Sunday ahead of a Russia-US summit this week where Kyiv fears President Vladimir Putin and President Donald Trump may try to dictate terms for ending the war between Russia and Ukraine.

Trump, who for weeks had been threatening new sanctions against Russia for failing to halt the war, announced instead on Friday that he would meet Putin on August 15 in Alaska.

A White House official has said Trump is open to Zelensky attending but preparations are underway for only a bilateral meeting.

"We've had no confirmation of that from the White House, but certainly Donald Trump covets the idea of that three-way meeting," RTHK's Washington correspondent Simon Marks told RTHK's Hong Kong Today programme.

"It's the Russians that are the problem in that regard because Vladimir Putin - through Kremlin aides - last week described a direct conversation between him and the Ukrainian leader as being something that was still miles away."

Russian strikes injured at least 12 in Ukraine's Zaporizhzhia region, the country's foreign affairs ministry said on Sunday.

Zelensky, responding to the strike, said, "That is why sanctions are needed, pressure is needed."

The Kremlin leader last week ruled out meeting Zelensky, saying conditions for such an encounter were "unfortunately still far" from being met.

Trump said a potential deal would involve "some swapping of territories to the betterment of both (sides)", compounding Ukrainian fears that it may face pressure to surrender land.

Zelensky says any decisions taken without Ukraine will be "stillborn" and unworkable.

On Saturday the leaders of Britain, France, Germany, Italy, Poland, Finland and the European Commission said any diplomatic solution must protect the security interests of Ukraine and Europe.

"The US has the power to force Russia to negotiate seriously," EU foreign policy chief Kaja Kallas said on Sunday.

"Any deal between the US and Russia must have Ukraine and the EU included, for it is a matter of Ukraine’s and the whole of Europe’s security."

EU foreign ministers will meet on Monday to discuss next steps, she said.

Nato Secretary General Mark Rutte told US network ABC News that Friday's summit "will be about testing Putin, how serious he is on bringing this terrible war to an end".

He added: "It will be, of course, about security guarantees, but also about the absolute need to acknowledge that Ukraine decides on its own future, that Ukraine has to be a sovereign nation, deciding on its own geopolitical future."

Russia holds nearly a fifth of the country.

Rutte said a deal could not include legal recognition of Russian control over Ukrainian land, although it might include de facto recognition.

He compared it to the situation after World War Two when Washington accepted that the Baltic states of Latvia, Lithuania and Estonia were de facto controlled by the Soviet Union but did not legally recognise their annexation. (Reuters/RTHK)