US President Donald Trump's peace plan needs improvement to make it acceptable for Ukraine and Europe, French President Emmanuel Macron told RTL radio on Tuesday.

A 28-point US peace proposal made last week caught many in the US government, Kyiv and Europe off-guard and prompted fresh concerns that the Trump administration might be willing to push Ukraine to sign a deal heavily tilted towards Moscow.

"It's an initiative that goes in the right direction: towards peace. However, there are aspects of that plan that deserve to be discussed, negotiated, improved," Macron said. "We want peace, but we don't want peace that is effectively a capitulation."

He added that only the Ukrainians could decide what territorial concessions they are ready to make.

"What was put on the table gives us an idea of what would be acceptable to the Russians. Does that mean that it is what must be accepted by the Ukrainians and the Europeans? The answer is no," Macron added.

Ukraine's first line of defence in case of peace with Russia would be regenerating its own army, and there can be no limit on it, Macron said. He also said frozen Russian assets are in Europe, and Europe alone can decide what to do with them.

The US plan would impose a limit on the size of Ukraine's army and give Washington some control of frozen Russian assets.

A few hours before a video call of the so-called "coalition of the willing" countries offering to assist post-war Ukraine, Macron also gave details on what a reassurance force might look like "far away from the front line" once fighting stops.

"There are British, French, Turkish soldiers who, the day peace is signed, so not in a context of war, are there to conduct training and security operations, as we do in certain countries on NATO's eastern flank," he said.

"We have about 20 countries that have already said what they are prepared to do actively, either in the air, on land, or at sea."