OSLO: Investigative journalists Maria Ressa of the Philippines and Dmitry Muratov of Russia won the Nobel Peace Prize on Friday for their tireless work in promoting freedom of expression at a time when liberty of the press is increasingly under threat.

Ressa, also a US citizen, is co-founder of Rappler, a digital media company for investigative journalism. Muratov is a co-founder of Russia's leading independent newspaper Novaya Gazeta.

The pair were honoured "for their efforts to safeguard freedom of expression, which is a precondition for democracy and lasting peace," said the chairwoman of the Norwegian Nobel Committee, Berit Reiss-Andersen.

"They are representatives of all journalists who stand up for this ideal in a world in which democracy and freedom of the press face increasingly adverse conditions," she said.

UN rights office congratulates all journalists on Nobel Peace prize

Ressa, 58, the only woman to win a Nobel so far this year, said the prize shows that "nothing is possible without facts," referring to the links between democracy and freedom of expression.

"A world without facts means a world without truth and trust," the outspoken critic of Philippines President Rodrigo Duterte told a livestreamed interview with Rappler.

She told Norwegian TV2 the honour would give her and her colleagues "tremendous energy to continue the fight."

Muratov dedicated his half of the prize to his newspaper's six journalists and contributors killed since 2000, who include the prominent investigative journalist Anna Politkovskaya.

"I can't take credit for this. This is Novaya Gazeta's," he was cited by Russian news agency TASS as saying. The newspaper on Thursday commemorated 15 years since Politkovskaya's killing.