The Kremlin said on Tuesday it was understandable that some countries were declining to take part in a Swiss-hosted peace summit on Ukraine this month because the gathering lacked clear goals and it was absurd to hold it without Russia.

Ukraine says more than 100 countries and organisations have agreed to attend the summit on June 15-16, to which Moscow has not been invited.

"This is a completely absurd activity, this is an idle pastime," Kremlin spokesman Dmitry Peskov told reporters. He said it was obvious the meeting was not geared towards results, and "that's why many countries don't want to waste time."

In a blow to Ukrainian President Volodymyr Zelenskiy, China has said it will not take part - something Russian parliament speaker Vyacheslav Volodin noted with satisfaction in a Telegram post on Tuesday.

He cited press reports saying Saudi Arabia would not go either, although the kingdom has not publicly announced its position on the summit. Peskov said that was a sovereign matter for Saudi Arabia.

The meeting is taking place at a crucial point in the third year of the war in Ukraine, where Russian forces have recorded a series of gradual gains since February.

In recent weeks a number of NATO countries have said they will allow Ukraine to strike targets inside Russia with weapons they have supplied to Kyiv, something that President Vladimir Putin has warned could escalate the war into a global conflict.

Russia says it is open to dialogue on the basis of the "new realities" it has created on the ground, where its forces control about 18% of Ukraine. Kyiv says peace can only be based on a full withdrawal of all Russian forces and the restoration of its territorial integrity. (Reporting by Reuters Editing by Ros Russell)