MUKALLA, Yemen (Reuters) - Since a Yemeni force trained and funded by the United Arab Emirates recaptured the southern port of Mukalla from al Qaeda fighters a year ago, the Gulf state's efforts to consolidate progress risks being compromised by traditional rivalries.
Divisions within Yemen's heavily tribal society as well as secessionist sentiment among troops and leaders in the once-independent south make building a truly national army an almost impossible task for the UAE right now.
They could also suck the UAE deeper into the Yemen quagmire.
UAE officers say the situation has made it difficult for them to push north and add to their territorial gains. A southern offensive has slowed down since it crossed the borders of Taiz province, they said.
"Taiz is part of the north, and southerners would not fight beyond their borders. Taking them there was a big challenge," one UAE military officer said.
The wealthy UAE is a powerful player in the Saudi-led military coalition fighting in a civil war that contains conflicts within conflicts.
The alliance backs President Abd-Rabbu Mansour Hadi's internationally-recognised government, based in Aden, against an Iranian-aligned Houthi rebel movement which holds the capital Sanaa.
More than 10,000 people have been killed since March 2015 and the country faces a humanitarian disaster as millions of people go hungry.
Hardline anti-Western groups al Qaeda and Islamic State have taken advantage of the chaos to press their own plans.
The capture of Mukalla from al Qaeda in April last year was a highpoint for the UAE–sponsored force. Lying on the Gulf of Aden, it is the capital of Hadramout province, which contains most of Yemen's oil resources.
The port once provided al Qaeda with millions of dollars in customs duties before the 30,000-strong force drove them into the nearby mountains.
Twelve months on, a semblance of normality has returned to the dusty, crowded streets although destroyed vehicles left by Al Qaeda fighters still lie on the roadsides and nervous young soldiers man checkpoints that suggest the fragility of their military gains.
The UAE concentrated its efforts on building a Yemeni force since it reduced its own troops' frontline exposure following a Houthi missile attack which killed scores of UAE and other Gulf soldiers in eastern Marib province in September 2015.
"I always knew how to handle weapons, but the UAE army taught us military discipline and gave us jobs," said Ahmed al-Khashaf, a lanky soldier in ill-fitting fatigues who was guarding the port.
Senior UAE military officers say their forces have trained and pay more than 11,000 Yemeni soldiers from Hadramout and 14,000 from Aden and three provinces. Unity is elusive, however.
"In Yemen, a Hadrami will fight only with another Hadrami. It is important to keep it in regional blocs when you build battalions," said a senior UAE military official, speaking on condition of anonymity.
But the war effort may now take second place to local fervour to revive a southern state, bolstered by the recapture of Aden from the Houthis by coalition forces in July 2015.
The former South Yemen, which had Aden as its capital, united with North Yemen in 1990 after a brief 1986 war.
Now local forces appear to be prioritising the fight on their front door over those in lands they regard as a foreign country.
"If there is no peace with the north, we will just split away," Hadramout provincial governor General Ahmad Bin Bourek said at his heavily guarded residence in Mukalla.
In Aden, 480 km (300 miles) to the west of Mukalla, divisions have already started to mount between Hadi and pro-secession troops.
Street protests have taken place against a decision by Hadi last week to sack Aidaroos al-Zubaidi, a secessionist and the UAE-backed governor of Aden.
The participation of masked fighters kitted out in UAE-issued military gear could render the Gulf state's involvement in Yemen's conflict even more complex.
Reporting By Aziz El Yaakoubi, editing by Sami Aboudi, William Maclean and Angus MacSwan