Donald Trump has confirmed that he and Vladimir Putin will discuss “land swapping” when they meet on Friday in Alaska for a high-stakes summit on the Ukraine war.

But the US president expressed frustration with Volodymyr Zelenskyy, the Ukrainian leader, for putting conditions on such a potential agreement.

During a news conference at the White House on Monday, Trump said he was frustrated with Zelenskyy’s insistence that Ukraine would need to hold a national referendum on any peace deal that stipulated recognising Russian control over territory that it has occupied during the war.

“I was a little bothered by the fact that Zelenskyy was saying I have to get constitutional approval,” Trump said. “He has approval to go to war and kill everybody but he needs approval to do a land swap. Because there will be some land swapping going on. I know that through Russia and through conversations with everybody.”

European diplomats have been taken aback by the lack of clarity on the US side about the territories Putin is demanding from Ukraine and the terms of a ceasefire. The discrepancies within the US reporting back on what Russia is seeking has alarmed European diplomats and only added to a fear that Trump, inflating his personal relationship with Putin, might make damaging concessions.

Describing his vision for a peace deal between Russia and Ukraine, Trump said an agreement would include “good stuff, not bad stuff, also some bad stuff for both”.

“We’re going to change the lines, the battle lines,” he added.

Trump, increasingly impatient with the Russian leader in recent months, has long said he does not see a ceasefire occurring until he meets Putin in person.

The German chancellor, Friedrich Merz, on Monday invited Trump to join emergency virtual talks with EU leaders and Zelenskyy on Wednesday, as European demands grow that the US president agree red lines before Friday’s summit with Putin.

Neither Zelenskyy nor European leaders have been invited to Trump’s meeting with the Russian president.

Trump said on Monday that he would also seek to arrange direct talks between Putin and Zelenskyy, a condition that the Russian president has rejected so far.

“The next meeting will be with Zelenskyy and Putin, or Zelenskyy and Putin and me. I’ll be there if they need, but I want to have a meeting set up between the two leaders,” Trump told reporters.

Merz’s office said in a statement that the virtual talks would focus on “further options for action to put pressure on Russia” and “preparations for possible peace negotiations and related issues of territorial claims and security”.

It is not clear whether or not Trump has accepted the invitation to the call.

EU foreign ministers were meeting in emergency session to underscore the demand. The UK has also been pressing for wider consultations after Trump unilaterally announced last week that he was pressing ahead with his first meeting with Putin since Russia’s invasion of Ukraine.

European leaders say Russia represents an existential threat to their continent and that they should not be excluded from the process. Issues such as the terms of a ceasefire, further sanction pressure on Russia, any proposed territorial swaps and security guarantees for Ukraine would be discussed with the US president in the virtual meeting. There is concern that an unpredictable Trump will be lured into making fatal concessions to Putin, and the meeting would be a chance for him to map out his strategy.

The Polish prime minister, Donald Tusk, said he was optimistic the US president would formally consult European leaders before his meeting, and that the summit between Trump and Putin filled him with hope and fear.

Brussels’ top diplomat, Kaja Kallas, in advance of the EU meeting, insisted: “President Trump is right to say that Russia must end its war against Ukraine. The United States has the power to force Russia to negotiate seriously.”

But, she said, “any agreement between the United States and Russia must include Ukraine and the EU because it is a security issue for Ukraine and for the whole of Europe.”

Radosław Sikorski, the Polish foreign minister, also asserted Europe’s relevance, saying: “Europe is paying for Ukraine to defend itself and we are sustaining the Ukrainian state. This is a matter of existential European security interests. We appreciate President Trump’s efforts but we will be taking our own decisions here in Europe.

“To get to a fair peace, Russia has to limit its war aims.”

The White House is insisting that the Alaska meeting is to gauge whether Putin is willing to make concessions for peace, including on accepting western security guarantees for Ukraine, an acceptance that would acknowledge the long-term legitimacy of the Kyiv government led by Zelenskyy.

Merz also spoke with Trump on Sunday night to underline that he would prefer the US to impose further economic sanctions on Moscow before the talks. He also said he assumed Zelenskyy would be involved in any talks, but for Moscow it would be a concession for a Russian delegation to hold talks with the Ukrainian president since its invasion is predicated on not recognising the legitimacy of the government.

A joint statement on Saturday from the leaders from France, Germany, Italy, Poland, Britain, Finland and the European Commission chief, Ursula von der Leyen, urged Trump to put more pressure on Russia and stressed: “The path in Ukraine cannot be decided without Ukraine.”

Putin will go into Friday’s talks believing he is making progress on the battlefield, Trump is desperate for a settlement and the Ukrainian people are also increasingly willing to make concessions for peace. But the Russian president also knows if he makes no substantive offer, Trump will be under real political pressure to go ahead with long-promised broader economic sanctions against Russia.

Lindsey Graham, the Republican senator behind the congressional plan to impose secondary sanctions on countries that trade with Russia, expressed confidence that Ukraine’s interests would be protected by Trump at the summit. He was involved in the weekend diplomacy and is trusted as an intermediary with Trump by Ukrainian officials. He said if Putin did not offer concessions he expected Trump to make countries importing Russian oil pay a “heavy price”, adding this applied not just to India, but also to China and Brazil. India is already due to face 50% tariffs later this month.

Speaking on NBC, Graham added: “Militarily, we need to keep Ukraine strong, keep flowing them strong and modern weapons, and security guarantees with European forces on the ground as tripwires to prevent a third [Russian] invasion. We want to end this with the sovereign, independent, self-governing Ukraine, and a situation where Putin cannot do this the third time without being crushed.”

He added: “I want to be honest with you, Ukraine is not going to evict every Russian, and Russia is not going to Kyiv, so there will be some land swaps at the end.”

Ukraine’s leadership has long said that de facto it will not recover all the territory it has lost in successive Russian invasions, but with European support it is fiercely resisting the Russian demand that it should hand over territory in the Donetsk region it has not yet ceded on the battlefield, especially if there are no security guarantees for Ukraine, or compensating land swaps by Russia.

Europeans are insisting that no limitations can be imposed on Ukraine developing its own military capabilities or the support it receives from third countries, including some inside Nato.