Yemen's former president said on Friday he would not negotiate with the government of President Abd-Rabbu Mansour Hadi, throwing into doubt the fate of peace talks on ending the conflict in Yemen which are due to restart later this month.

Ali Abdullah Saleh, who enjoys the loyalty of the armed forces despite having stepped down from office nearly four years ago after months of protests, had joined forces with the Iran-allied Houthis in fighting a Saudi-led alliance trying to shore up Hadi.

The warring sides held the latest round of peace talks in December but failed to find a political solution that would end the conflict, which has killed nearly 6,000 people. Negotiations are set to resume on January 14.

"There will be no dialogue with the mercenaries who are seeking power ... there will only be dialogue with the Saudi regime," Saleh said in a television address on his television station, Yemen Today.

A coalition led by Saudi Arabia and its Sunni Muslim allies has been fighting the Shi'ite Houthi movement, which controls the capital, since March 2015.

The United Nations said UN Yemen envoy Ismail Ould Cheikh Ahmed was in Riyadh and would be travelling to Sanaa "soon".

Riyadh sees the Houthis as a proxy for bitter regional rival Iran to expand its influence. They deny this and say they are waging a revolution against a corrupt government and Gulf Arab powers beholden to the West.

A growing diplomatic dispute between Riyadh and Tehran, triggered by Saudi Arabia's execution of a prominent Shi'ite cleric, has damaged the outlook for any resolution to the conflict in the Arabian Peninsula nation.-Reuters