Hundreds of thousands of Yemenis descended on Sanaa on Thursday in a major show of force for former president Ali Abdullah Saleh, whose alliance with the country's Houthi rebels has been shaken by mutual distrust.

Tensions have been rising between Saleh and his one-time foe, rebel chief Abdul Malik al-Houthi, who joined ranks in 2014 in a shock alliance that drove the Saudi-backed government of Abd Rabbu Mansour Hadi out of the capital and into the southern province of Aden.

The rally marking 35 years since the founding of Saleh's Arab nationalist General People's Congress (GPC) sends out a signal that the strongman remains a force to be reckoned with.

Crowds filled the four-square-kilometre square and poured into the streets of the capital, waving the blue flag of the GPC and carrying pictures of the 75-year-old Saleh.

Saleh ruled Yemen with an iron fist for more than three decades before stepping down in 2012 after a bloody year-long uprising.

But the strongman retained the loyalty of some of the best-equipped units in the military and later joined forces with the Houthis, after they overran the capital in 2014.

The ensuing civil war between the Saudi-backed government and the Houthi-Saleh alliance has killed thousands and brought the Arabian Peninsula country to the brink of famine.

Saleh's supporters had travelled to Sanaa from across the impoverished country, camping out in Sabaeen Square overnight ahead of the rally.

An AFP reporter in Sanaa said the Houthis had set up checkpoints at the main entrances to the city. But they did nothing to stop the demonstrators from reaching the square, where the rebels had also deployed but did not interfere with the rally.

Saleh, who survived the Arab Spring protests that saw a string of his peers ousted from Egypt to Libya, appeared in person at the rally and gave a brief speech behind bulletproof glass, surrounded by heavily armed guards.

“We are political pioneers with a solid anchor, and we have been facing conspiracies against us since 2011,” he told the cheering crowd, referring to the start of protests in Sanaa that eventually led to his resignation.

'Allies for show'

Saleh said he was ready to deploy “tens of thousands of fighters to the frontlines”, on the condition that the rebel-led government train and pay them.

Analysts have said the rally serves in part as public protest against the Houthis, who with Saleh have run the capital since 2014.

The rebels have rapidly risen in a parallel government in Sanaa, and now hold clout in the city's economy, defence and educational ministries. Former troops and civil servants in the parallel rebel-run government have not been paid for months.

Saleh's second-in-command in the GPC, Aref al-Zouka, on Thursday criticised the Houthis for financial mismanagement and corruption, saying the party refused to be “allies for show”.

A war of words between Saleh and Abdul Malik al-Houthi, whose rebel group have historically clashed with Saleh's troops, has escalated in the past week.

The two have publicly accused each other of treason, with Saleh hinting his allies were merely “a militia” and the rebels warning the former president he would “bear the consequences” of the insult.

The Houthis reportedly suspect Saleh has been negotiating with a Saudi-led Arab coalition that supports the Yemeni government.

Saleh was a strong ally of Saudi Arabia from the late 1970s, when he fought the Houthis for control of Yemen, until 2014.

The Saleh camp has meanwhile accused the Houthis of aiming to consolidate their power in Sanaa.

The war between the government of Hadi, allied with a Saudi-led Arab military coalition, and the allegedly Iran-backed rebel camp has killed more than 8,300 Yemenis since 2015 and pushed the country to the brink of famine.

More than 30 people, including civilians, were killed on Wednesday in air raids on Sanaa, where the Saudi-lead coalition has been bombing the Houthis since joining the war in 2015.

A cholera outbreak has independently claimed an estimated 2,000 lives since April in Yemen.