The Kremlin yesterday questioned the tone of a letter sent by US President Donald Trump to his Turkish counterpart Tayyip Erdogan, saying it was highly unusual for correspondence between heads of state.

The White House on Wednesday released the Oct 9 letter, in which Trump (photo) urged Erdogan to halt Turkey's cross-border offensive into northeast Syria, saying "Don't be a tough guy" and "Don't be a fool!"

"Let's work out a good deal!" the letter said.

"You don't often encounter such language in correspondence between heads of state. It's a highly unusual letter," Kremlin spokesperson Dmitry Peskov told reporters on a conference call.

Moscow's ties with Washington are at post-Cold War lows, but the Kremlin is usually careful not to call into question actions by Trump, whom Russian politicians often cast as a positive force in ties who is held back by an anti-Russian US establishment.

The letter was released as Trump battled to control political fallout after his decision to withdraw US troops from northern Syria, clearing the way for Turkey's operation against Washington's Kurdish allies.

- Reuters