An alliance between Yemen's Houthis (Ansarallah) and former president Ali Abdullah Saleh, which jointly controls Sanaa, has begun to unravel, threatening to further splinter the country.
Witnesses say armed supporters of Saleh and the Houthis have spread across the city on the eve of a mass rally to mark the 35th anniversary of Saleh's General People's Congress, sparking fears of an intensification of violence.
For three years, the Saleh-Houthi alliance has fought the government for control of Yemen in a war that has brought the country to the brink of starvation.
Tension between Saleh and the Houthis is at an unprecedented high, threatening an unlikely alliance that has long been viewed as tactical at best.
The two sides have flung mutual accusations of treason over the past week, culminating Wednesday (August 23rd) in an open threat by the Iran-backed Houthis, who said Saleh would have to "bear the consequences" after he dismissed his allies as "militias" in a weekend speech.
Complex history with the Houthis
Saleh's history with the Houthis is long and complicated.
He has waged six wars against the Houthis since the late 1970s, when he was president of then-independent north Yemen and allied with Saudi Arabia, which leads the coalition now backing President Abd Rabbu Mansour Hadi.
Saleh was elected Yemen's first president when the country unified in 1990 and remained in power until 2012, resigning after a year of protests in a deal brokered by the Gulf Co-operation Council (GCC) that guaranteed him immunity.
He was succeeded by Hadi, then vice president, who emerged as his biggest political rival.
Saleh in 2014 realigned himself with Abdul Malik al-Houthi, a leader of the Houthis with ties to Iran.
The Houthis drove the Hadi government out of Sanaa and into Aden.
Saleh and al-Houthi continue to control Sanaa, where the former president's influence has not waned five years after his reluctant resignation.
By 2016, Saleh had reached a power-sharing pact with the Houthis and ran a parallel government from Sanaa in an alliance insiders and analysts have long warned would not last.
United by a common enemy
"On both ends, it has been a common enemy... keeping both sides together," said Adam Baron, a fellow at the European Council on Foreign Relations.
"With the expulsion of the Houthis from much of the south, that common enemy has disappeared; thus, it is not shocking that the grudging alliance between southern secessionists and the internationally backed government has devolved into deep tensions."
The power-sharing pact began to come apart in April, when Hadi fired Aden governor Aidarous al-Zoubeidi and Hani bin Breik, a member of his cabinet.
Both al-Zoubeidi and bin Breik have historically favoured reinstating southern Yemen's autonomy, and went on to announce the establishment of the Southern Transitional Council, with support from local communities and reportedly from the UAE, a key player in the coalition.
Saleh is also drawing on his popular reach in Sanaa, which until 2014 had been largely off-limits to the Houthis, confined to the northern Saada province.
Saleh and the Houthis have had a tacit agreement in sharing Sanaa: the ex-president lacks the muscle the Houthis can provide, and Saleh's structural and popular power in the capital is unparalleled.
That delicate power balance may be tested in Thursday's rally, which Saleh has said will be a demonstration of support for "legitimacy" in Yemen.
'Mosaic of alliances'
Analysts say both Saleh and the residents of Sanaa are not happy with the Houthis, who control the defence ministry and military intelligence.
"People are not necessarily coming out in support of Saleh, but in protest against the Houthis," said Yemeni analyst Maged al-Madhaji, director of the Sanaa Centre for Strategic Studies.
"The Houthis are well aware that Saleh needs them, so over the past year-and-a-half they have worked on the military, political and social fronts to try and gain some of the popular support that Saleh has."
This, coupled with reports that Saudi Arabia is looking to cut back on its involvement in the Yemen war, may spell the end of what analyst Baron calls an "alliance of convenience" between Saleh and the Houthis.
Speaking on condition of anonymity, a source in Saleh's General People's Congress said attempts to mediate this week with the Houthis had failed.
The source also said Saudi Arabia would be happy to see its former ally split from the Houthis, but was not yet ready to take Saleh back into the fold.
"Effectively, the conflict in Yemen has never been a two-sided war -- this is something that has been characterised by a mosaic of alliances of convenience from the start," said Baron.
"All things are possible in Yemen, and there have definitely been feelers going out in all sorts of directions for some time now."