Russian President Vladimir Putin is open to discussing a Ukraine ceasefire deal with Donald Trump but rules out making any major territorial concessions and insists Kyiv abandon ambitions to join NATO, five sources with knowledge of Kremlin thinking told Reuters, the latter reports.

US President-elect Trump, who has vowed to swiftly end the conflict, is returning to the White House at a time of Russian ascendancy. Moscow controls a chunk of Ukraine about the size of the American state of Virginia and is advancing at the fastest pace since the early days of the 2022 invasion.

In the first detailed reporting of what President Putin would accept in any deal brokered by Trump, the five current and former Russian officials said the Kremlin could broadly agree to freeze the conflict along the frontlines.

There may be room for negotiation over the precise carve-up of the four eastern regions of Donetsk, Luhansk, Zaporizhzhia and Kherson, according to three of the people who all requested anonymity to discuss sensitive matters.

Russia may also be open to withdrawing from the relatively small patches of territory it holds in the Kharkiv and Mykolaiv regions, in the north and south of Ukraine, two of the officials said.

Putin said this month that any ceasefire deal should reflect the "realities" on the ground but that he feared a short-lived truce which would only allow the West to rearm Ukraine.

Two of the sources said outgoing US President Joe Biden's decision to allow Ukraine to fire American ATACMS missiles deep into Russia could complicate and delay any settlement - and stiffen Moscow's demands as hardliners push for a bigger chunk of Ukraine. On Tuesday, Kyiv used the missiles to strike Russian territory for the first time, according to Moscow which decried the move as a major escalation.

If no ceasefire is agreed, the two sources said, then Russia will fight on.