UN Secretary-General Antonio Guterres on Thursday called on Yemen's warring sides to engage in UN-brokered talks without imposing pre-conditions afer the government and rebels put forward demands.

Yemen's government and Houthi rebels began talks in Sweden on Thursday aimed at ending nearly four years of war that have pushed the impoverished Arab country to the brink of mass starvation.

Guterres "urges the parties to make progress on the agenda for the consultations ... by exercising flexibility and engaging in good faith and without pre-conditions," said a UN statement.

The UN chief appealed to the sides to continue the de-escalation of Hodeida, the rebel-held port city that is a key entry point for humanitarian aid and vital supplies.