The Kremlin says the tone in the letter the US President sends to his Turkish counterpart is very unusual.

"You don't often come across such language in correspondence between heads of state. It's a very unusual letter," Kremlin spokesman Dmitry Peskov told reporters at a news conference in Moscow. Today, referring to the letter of US President Donald Trump to Turkish President Recep Erdogan on October 9.

Relations between Moscow and Washington were low after the Cold War, but the Kremlin is often careful not to question Trump's actions.

The White House on October 9 published the content of the letter, in which Trump urged Erdogan to stop attacking northeastern Syria, advising the Turkish leader "not to be stubborn or goofy". Trump also called for Erdogan to better reach a deal with the Kurds in Syria.

The letter was published by the White House as an explanation in the context of the US president being considered "green light" for Turkey to conduct military operations in Syria. Many US lawmakers sharply criticized the decision to withdraw 1,000 troops from Syria before Ankara attacked the Kurds.

British media today quoted unnamed sources from Turkish officials as saying that Erdogan rejected Trump's offer and threw a letter in the trash. Washington and Ankara have not yet spoken about this information.