Clashes between Yemeni loyalist forces and rebels have killed 13 fighters, military sources said Tuesday, as the UN chief urged warring parties to begin delayed peace talks.

UN-brokered peace talks, which were set to open in Kuwait on Monday, were delayed after the insurgents failed to show up over alleged Saudi violations of a ceasefire that took effect on April 11.

Fighting erupted late Monday in Marib province, east of the rebel-held Yemeni capital Sanaa, with warring parties trading blame for the ceasefire breaches.

Five soldiers loyal to President Abedrabbo Mansour Hadi and eight rebel fighters were killed in the clashes which continued intermittently through Tuesday, the pro-government military sources said.

They said the fighting erupted when the Iran-backed Houthi rebels and their allies tried to capture positions held by loyalist troops.

The toll could not be independently confirmed.

Sporadic fighting was also reported in other areas, including Nahm northeast of Sanaa and in the southwestern province of Taez.

At the United Nations, Secretary General Ban Ki-moon urged the Gulf-backed government and the Shia Houthi rebels and their allies to engage with his envoy "so that talks can start without further delay".

Pro-Hadi chief-of-staff General Mohammed Ali al-Maqdishi slammed the rebels for "not respecting" the ceasefire which he said his forces were committed to.

"The truce is still holding based on orders from our political leadership," said Maqdishi.

The rebels meanwhile accused loyalist forces of launching attacks and dispatching reinforcements to several provinces, in a statement on their sabanews.net website.

They also said warplanes belonging to the Saudi-led coalition, which has intervened militarily in support of loyalists since March last year, flew sorties over several areas of Yemen despite the ceasefire.

In a statement on Facebook late Monday, rebel spokesman Mohammed Abdulsalam said "we affirm our continued commitment to dialogue... and this is why our demand from the first day was for talks to be held in an atmosphere of calm, peace, and stability."

"But unfortunately, since April 11, the aggression hadn't stopped and the air strikes have continued on several areas," he said.

UN envoy Ismail Ould Cheikh Ahmed and government representatives were still in Kuwait on Tuesday, according to officials close to the government delegation.

Previous attempts at peace talks -- including a failed round in January -- have been unable to stop Yemen's conflict, which the United Nations says has killed more than 6,400 people and forced almost 2.8 million from their homes.

Jihadists including from Al-Qaeda in the Arabian Peninsula, the powerful Yemeni branch of the extremist network, have exploited the conflict to seize territory and gain influence.

On Tuesday, a suicide bomber blew himself up before reaching a security checkpoint in main southern city Aden, where jihadists have carried out deadly attacks against pro-government forces in recent months, a security official said.

There were no casualties apart from the assailant himself, said the official, describing the bomber as "an extremist".