Serbia's president said Friday he doesn't share U.S. President Donald Trump's optimism that an agreement between Serbia and Kosovo is "within reach," two decades after their war.

Serbian President Aleksandar Vucic said that a letter sent by Trump expressing that opinion is "rational" and welcome, but also added: "We are far from any kind of agreement."

In almost identical letters to the Serbian and Kosovo leaders, Trump urged the two to secure a "historic" deal that would bring "long-sought" peace to the Balkan region.

Trump said that the U.S. stands ready to assist and that he is looking forward to hosting the two presidents in the White House "to celebrate what would be an historic accord."

Kosovo broke away from Serbia after a 1998-99 war and NATO intervention that stopped a bloody Serbian crackdown against Kosovo Albanian separatists. In 2008, Kosovo unilaterally declared independence which is recognized by the U.S. and most of the West, but not by Serbia and its allies Russia and China.

Serbia and Kosovo have been conducting European Union-mediated talks aimed at normalizing relations. Trump's letter is seen as sign that Washington is willing to take a more active role in mediating between the two foes.

"Don't forget that America has recognized Kosovo's independence and that America will not easily change that decision," Vucic said at a joint press conference with Greek Prime Minister Alexis Tsipras.

"What is good in all this is that America is insisting on Belgrade's role and tells Pristina that it has to make an agreement with Serbia. That's maybe good news for us," Vucic said.

Tsipras said he supports the EU-sponsored dialogue in Brussels and urged Serbia and Kosovo to work out a compromise "where there would be no winners or losers."

Asked whether Russia could oppose any Trump initiative in the region, Vucic said he has not seen any negative reaction from Moscow, announcing that Russian President Vladimir Putin is arriving in Belgrade for an official visit on Jan. 17.