Volodymyr Zelensky raised the possibility of Ukrainian troops occupying Russian villages, according to leaked US intelligence.
Quoting fresh details from a Pentagon intelligence leak earlier this year, The Washington Post reported that Mr Zelensky has been far more hawkish about attacking Russia than previously thought.
To receive long-range weapons from the West, including British Storm Shadow cruise missiles that were fired for the first time in Ukraine this weekend, Mr Zelensky has vowed not to attack Russia.
But the unearthed US intelligence reveals that Mr Zelensky told Ukrainian officials that he wanted to bomb an oil pipeline running from Russia to Hungary, a Nato member, and also hit targets hundreds of miles inside the Russian border.
The intelligence broadly relates to three meetings between Mr Zelensky and his staff this year.
At a meeting in January, Mr Zelensky reportedly suggested that Ukraine should “conduct strikes in Russia” and “occupy unspecified Russian border cities”.
The document, which was marked as “Top Secret”, said that the aim of the attacks was to give Kyiv bargaining chips in future talks with the Kremlin.
In another meeting in late February, Mr Zelensky reportedly “expressed concern” that Ukrainian missiles don’t have the range to hit “Russian troop deployments in Russia” and that Ukraine should launch drone attacks on “unspecified deployment locations in Rostov”.
Mr Zelensky was further said to have suggested that Ukraine should blow up the Druzhba (Friendship) pipeline in Russia that runs to Hungary. Viktor Orban, the Hungarian prime minister, has been far more lenient towards the Kremlin’s position over its invasion of Ukraine than other European countries.
“Zelensky highlighted that … Ukraine should just blow up the pipeline and destroy Hungarian Viktor Orban’s industry, which is based heavily on Russian oil,” the document said.
In the leaked document, Mr Zelensky noted that Zelensky could have been “expressing rage toward Hungary and therefore could be making hyperbolic, meaningless threats”.
Ukrainian special forces are believed to have made small incursions into Russia but the Ukrainian government has always denied responsibility for drone attacks deeper inside Russia. These attacks have included striking airfields close to Moscow and even the Kremlin itself, in the centre of the Russian capital.
Now Russian commentators have pounced on The Washington Post report as proof that Mr Zelensky is threatening Russia itself.
“The Washington Post confirms that Zelensky is keen to take over some settlements in uncontested Russian territory such as the Bryansk and Belgorod regions,” said Sergei Markov, a former Kremlin adviser.
“Zelensky worked out such a plan with British intelligence,” he added.
In April, US security services arrested a 21-year-old airman at his home in Massachusetts and charged him with leaking classified intelligence documents which were circulated on the Discord website.
The Pentagon did not deny the reports to The Washington Post.
Responding to The Washington Post reporting, Mr Zelensky said: “We are not attacking Russian territory. We have neither the time nor the strength to do this, and we do not have extra weapons to do so.”
He was speaking at a press conference in Berlin after meeting the German leader and accepting a military aid package worth around £2.3 billion.
The documents also allege that Mr Zelensky directed his aides to abort planning attacks on Russian forces in Syria with the secret help of the Kurdish.