Five years after Saudi Arabia intervened in Yemen's civil war, leading a military coalition to prop up the government which had been driven out of its capital, the Huthi rebels are only stronger, more resilient and gaining ground.
The Iran-aligned insurgents' capabilities have developed in the past year, with attacks on strategic targets in Yemen and neighbouring Saudi Arabia using sophisticated drones.
Experts say that pressure on the Saudis to reduce civilian casualties in air strikes, a drawdown by their coalition partner the United Arab Emirates' in mid-2019, and rifts within the government camp, have strengthened the rebels' resolve.
The novel coronavirus sweeping the world could be a wild card in the conflict. Saudi Arabia has reported hundreds of cases and imposed tough lockdown measures, while Yemen appears highly vulnerable even if its broken healthcare system has not yet registered any cases.
But after military victories in recent months that have given them the upper hand, the sixth year of the conflict is likely to deliver more gains to the rebels, and more hardship to civilians who have endured the long war.
Who are the Huthis?
The Huthi tribal fighters belong to the Zaidi minority, an offshoot of Shiite Islam, that makes up a third of Yemen's Sunni-majority population. They rose up in the 1990s over alleged sectarian discrimination.
The movement is named after its late spiritual leader Badreddin al-Huthi and his son Hussein, who was killed by Yemeni government forces in 2004.
Between 2004 and 2010, the group -- known as Ansarullah (Supporters of God)-- fought six wars against Yemen's then-government and battled Saudi Arabia in 2009-2010 after storming across the border.
They also took part in protests that forced veteran ruler Ali Abdullah Saleh from office in 2012 but later formed an alliance with him before again falling out and killing him in 2017.
The Huthi ouster of the government of Yemeni President Abedrabbo Mansour Hadi and takeover of the capital Sanaa set off the Saudi-led intervention in March 26, 2015.
Since then, the coalition has not been able to defeat the insurgents, who have none of their adversaries' high tech firepower but are well-trained, tenacious and accustomed to battling in Yemen's harsh and mountainous terrain.
Who arms them?
The Huthis have a range of military equipment and weapons, including tanks and ballistic missiles, that they seized from Yemeni army depots after taking control of the capital. They also claim to manufacture and develop their own arms.
Last year, they showed off at least 15 unmanned drones and various missiles, including long-range models they say can hit targets as far as 1,500 kilometres (about 900 miles) away.
In September 2019, the Huthis claimed responsibility for unprecedented strikes on Saudi Aramco oil facilities, but Riyadh and Washington blamed Tehran, saying the rebels did not have the capability.
Saudi Arabia and the US have long said that the Huthi militia is an Iranian "tool" and accused the Islamic republic of supplying them with weapons, a charge Tehran denies.
Secret of their success?
The UAE, disillusioned with what is fast becoming the Gulf's own "forever war", pulled back its troops in July last year in a blow for the coalition. Meanwhile a heavy civilian toll in Saudi air strikes, which drew UN accusations of violations that could amount to war crimes, forced the regional power to take a step back.
"Government forces have been greatly weakened by the sharp reduction in coalition air strikes and the withdrawal of key Emirati 'enablers'," the Washington Institute said in a recent report. "This drawdown lessened the military pressure on the Huthis."
Divisions in the anti-Huthi camp -- notably in the south where fighting between separatists and forces loyal to the government threatened to create "a civil war within a civil war" -- also strengthened the rebels' hand.
During that time, they were able to rapidly switch elite forces between different fronts with the help of advisors from the Lebanese militia Hezbollah, increase the use of precision rocket and drone strikes, and "consolidate their new territorial gains via tactical minefields", the Washington Institute said.
What does the future hold?
"The Iran-backed Huthis are consolidating their power in Yemen," the Middle East Institute said in a recent report.
A Yemeni government military official, who spoke to AFP on condition of anonymity, conceded that the rebels "have become stronger than ever".
The Huthis took control of the capital of the northern province of Al-Jawf earlier this month -- a strategic loss that means they now threaten oil-rich Marib province, the source of significant revenue.
"Yemen's political map is set to change dramatically," the International Crisis Group said this month of the prospect of the government losing its last stronghold in the north.