By Guy Faulconbridge and Andrew Gray

MOSCOW/BRUSSELS (Reuters) -The Kremlin on Monday said a call by Pope Francis for talks to end the Ukraine war was "quite understandable", but NATO's boss said now was not the time to talk about "surrender".

Pope Francis said in an interview recorded last month that Ukraine should have "the courage of the white flag" to negotiate an end to a conflict that has killed tens of thousands.

As the West grapples with how to support Ukraine and the prospect of a sharp change in U.S. policy if Donald Trump wins November's presidential election, Putin has essentially offered to freeze the battlefield along its current front lines, a premise Ukraine rejects.

"It is quite understandable that he (the pope) spoke in favour of negotiations," Kremlin spokesman Dmitry Peskov told reporters.

He said President Vladimir Putin had repeatedly said Russia was open to peace talks:

"Unfortunately, both the statements of the pope and the repeated statements of other parties, including ours, have recently received absolutely harsh refusals."

Russia says it sent its troops across the border in February 2022 in a "special military operation" to ensure its own security. Kyiv and the West call it a brutal colonial-style war of conquest.

Moscow's offers to negotiate have invariably been predicated on Kyiv giving up the territory that Moscow has seized and declared to be part of Russia, amounting to more than a sixth of Ukraine.

Peskov said Western hopes of inflicting a "strategic defeat" on Russia were "the deepest misconception", adding: "The course of events, primarily on the battlefield, is the clearest evidence of this."

But NATO Secretary General Jens Stoltenberg said negotiations that would preserve Ukraine as a sovereign and independent nation would only come when Putin realised that he would not win on the battlefield.

"If we want a negotiated, peaceful, lasting solution, the way to get there is to provide military support to Ukraine," he told Reuters at NATO headquarters in Brussels.

Asked if this meant now was not the time to talk about a white flag, he said: "It's not the time to talk about surrender by the Ukrainians. That will be a tragedy for the Ukrainians."

He added: "It will also be dangerous for all of us. Because then the lesson learned in Moscow is that when they use military force, when they kill thousands of people, when they invade another country, they get what they want."

Ukraine on Sunday rebuffed Francis's call to negotiate an end to the war. President Volodymyr Zelenskiy said the pontiff was engaging in "virtual mediation" and his foreign minister said Kyiv would never capitulate.

Zelenskiy, who signed a decree in 2022 ruling out talks with Putin, said last week that Russia will not be invited to a peace summit due to be held in Switzerland.

(Reporting by Reuters;Editing by Andrew Osborn and Kevin Liffey)