At least 17 people have been killed in fighting between Houthi rebels and tribal fighters in Yemen's Ibb province, despite a 24-hour ceasefire agreement between the warring sides.

Saturday's escalation in violence comes after tribesmen set up a checkpoint in Yareem town, to prevent the Houthis from entering the provincial capital of Ibb in central Yemen.

Sources told Al Jazeera that there had been hours of calm in the city after a 24-hour ceasefire was agreed after tribal mediation between the Houthis and Tribesmen.

The city of Ibb, 150km south of Sanaa, borders Bayda province, a stronghold of al-Qaeda in the Arabian Peninsula (AQAP), where Houthis have clashed repeatedly with al-Qaeda linked fighters since Tuesday.

The Houthis, who took over Sanaa on September 21, and who have held the strategic southern port of Hudaydah since Tuesday, did not face any opposition from local authorities as they entered the provinces of Dhamar and Ibb and set up checkpoints, officials said.

'Utter chaos in every corner'

The Houthi advance has increased fears of an outright sectarian warfare in the north and in a separate sign of the fragility of Yemen's embattled state, southern separatists seeking to split from the north set an ultimatum for the government to evacuate its soldiers and civil servants by November 30.

Al Jazeera's Omar al-Saleh, reporting from the capital city of Sanaa, said that due to the rebels making new gains every day and the secessionist movement in the south, there was "utter chaos in every corner of the country".

"Many Yemenis are now worried that there could be a sectarian war in the north and a secessionist war in the south," al-Saleh said. "The secessionists in the south are now taking advantage of the chaos in the north and they are demanding self determination and full independence of the south of Yemen."

The Houthis, who hail from the northern highlands and champion the interests of the Zaidi community which make up one fifth of Yemen's 25 million population, are increasingly imposing their authority outside the capital as well as in it.

The group wants the northern part of the country to be one region instead of three and are also seeking a bigger say in drafting the constitution.

Al Jazeera