Volodymyr Zelensky has called for a face-to-face meeting between himself and Vladimir Putin in a renewed bid to end the war.
In an open letter to the Russian president, the Ukrainian leader said it would be "wrong to simply wait" until the war in Europe becomes the focus of the US's attention once more, adding peace could only come "through direct engagement between" Ukraine and Russia.
He also called for a full ceasefire for the duration of proposed negotiations - something Putin ruled out earlier on Thursday.
US President Donald Trump said on Thursday he thought "it would be great" if the two leaders met.
The Kremlin confirmed it had received the letter and Putin would be briefed on it.
The tone of the letter was defiant, even mocking, drawing attention to Ukraine's recent strikes on Russian territory.
Zelensky stated that "after 26 years in power, age is beginning to take its toll" on Putin.
The letter also provided an invitation.
"Ukraine proposes ending this war through direct engagement between us — and you. I am proposing a meeting," Zelensky wrote.
It's not a new offer from Ukraine's leader.
As it has before, the Kremlin responded, saying Zelensky was welcome to meet Putin in Moscow.
What was notable was Kyiv's public acknowledgement that the US "is fully focused on the issue of Iran".
"It would be wrong to simply wait until the war in Europe returns to the centre of its attention," Zelensky wrote.
Speaking to foreign journalists in St Petersburg, without apparently having seen the contents of the letter, Putin said he was "certainly prepared and willing to reach an agreement with Ukraine", but said compromises needed to be made.
Putin suggested that as Trump was busy with Iran, the EU could talk Zelensky into surrendering territory.
Putin's longstanding position has been that Ukraine should withdraw from four regions partially occupied by Russia - Donetsk, Luhansk, Kherson and Zaporizhzhia - and give up its efforts to join Nato.
Ukraine has ruled out ceding territory, saying it would embolden Russia to invade again, as it had in 2022 when it launched its full-scale war eight years after illegally annexing Crimea.
Ceasefire negotiations have stalled in recent months, and previous peace talks in Geneva, Abu Dhabi and Istanbul have failed.
In the letter, which is more than 1,800 words long, Zelensky said: "It is not as if we in Ukraine are concerned about the fate of Russian soldiers after everything your war has brought to our country.
"But I do care about Ukrainians. We are losing our people, and every loss is painful to us."
Zelensky said Russians had become tired of Ukrainian drone and missile attacks, petrol shortages and rising prices, as well as war.
"Do not be afraid to take the path out of this war. That is the main thing that is required of you now," he implored.
He said Ukraine was proposing to end the war "through direct engagement between us".
Zelensky said face-to-face negotiations could take place in a country such as Switzerland or Turkey.
Ukrainian foreign minister Andriy Sybiha, said "this open letter is a serious and meaningful proposal to end the war".
"We expect a meaningful response to this proposal. It's time to end this war. It's time to choose peace," he added.
The Ukrainian president's letter came on the same day Putin was in St Petersburg, where a major economic forum is taking place.
The previous day Kyiv had launched a drone attack on the city's outskirts, a strike mentioned in Zelensky's message as "paying a visit".
Separately Russian-backed authorities in occupied Crimea blamed Ukraine for the death of four people in attacks on Simferopol. Ukraine said it had hit a fuel depot.
During his press conference on Thursday, Putin appeared to immediately cast doubt on whether a meeting or deal could ever take place.
"Whether Mr Zelensky is a legitimate representative of Ukraine, this is a question for the lawyers, for a legal analysis," he said.
Trump said he thought the US had been instrumental in bringing the two countries closer to peace.
"I think it would be great if they met. They should. Get it done," he said.
Asked about the compromises the two sides would have to make, he said he would "rather not say".
"I want them each to make certain compromises, and I think they're going to do it."
