Yemeni President Abedrabbo Mansour Hadi threatened Sunday to boycott peace talks with Iran-backed rebels if the UN envoy insists on a roadmap stipulating a unity government that includes the insurgents.

UN-sponsored talks between Hadi's Saudi-backed government and the Huthi rebels and their allies are scheduled to resume on Friday in Kuwait after a two-week break.

More than two months of negotiations have failed to make headway to end the deadly conflict.

"We will not return to the talks in Kuwait if the United Nations tries to impose the latest proposal by mediator Ismail Ould Cheikh Ahmed," Hadi said during a visit to inspect troops in Marib province, east of the rebel-held capital.

Ould Cheikh Ahmed has put forward a peace roadmap that would see the formation of a unity government and the withdrawal and disarmament of the rebels.

He said the negotiators had welcomed his proposal but had not agreed a timetable or the steps needed to implement it.

The government had already expressed doubts this month about the UN-backed efforts.

Hadi's government wants to re-establish its authority across the entire country, much of which is rebel-controlled, and restart a political transition interrupted when the Huthis seized Sanaa in 2014.

The rebels have conditioned their withdrawal on both sides agreeing on a new president to manage the transition.

In his speech, published on the official sabanew.net website, Hadi insisted that the rebels were using the Kuwait talks to "legitimise their coup d'etat", and rejected the UN proposal for a unity government.

"The UN has tried to convince us to form a coalition government. We said we would issue a statement declaring our boycott of the Kuwait consultations," Hadi said.

"The Yemenis will not allow Yemen to be turned into a Persian state" in Iran's orbit, he said, vowing to recapture Sanaa "soon".

In February last year the Huthis dissolved the government and parliament and formed their own Supreme Revolutionary Committee to rule Yemen.

Ould Cheikh Ahmed has urged both sides to make concessions to end the conflict, which has cost more than 6,400 lives since March 2015 when a Saudi-led coalition intervened to push back the rebels.

Hadi's visit to Marib comes as fighting raged on between loyalists and rebels in the province's northern oil-rich region of Sarwah.

Late Saturday, Saudi-led coalition defence systems intercepted a ballistic missile fired by the rebels at Marib city, a military source said.

Coalition forces have sent military reinforcements including troops, tanks and other armoured vehicles into the province in recent days in what military sources described as preparations to retake Sanaa and surrounding areas.

In Nahm, northeast of Sanaa, coalition air raids and fighting have killed six rebels and three loyalists over the past 24 hours, military sources said.

Other clashes have taken place in Jawf province near the border with Saudi Arabia.

The fighting in Yemen has continued despite a ceasefire coming into effect on April 11.