The Paris climate deal will be less effective without its key participants, the Kremlin said on Thursday, commenting on an expected announcement by U.S. President Donald Trump on whether to keep Washington in the global pact to fight climate change.

A source close to the matter has said Trump, with whom Russia wants better ties, is preparing to pull out of the accord.

"President (Vladimir) Putin signed this convention in Paris. Russia attaches great significance to it," Kremlin spokesman Dmitry Peskov told a conference call with reporters.

"At the same time, it goes without saying that the effectiveness of this convention is likely to be reduced without its key participants."