Two months after Yemen's truce expired, fighting largely remains on hold but a series of attacks by Huthi rebels could have serious repercussions for a country crippled by war.

At least three drone strikes at ports on Yemen's southern coast have disrupted oil exports, the main source of income for the Arab world's poorest country and its Saudi-backed government.

The strikes launched by the Iran-backed rebels since late October caused no casualties but stopped some tankers from docking at the government-controlled harbours of Qena and Al-Dabah.

They followed the failure to extend a UN-brokered truce that was in place for six months until October 2 and had brought a much-needed pause in the seven-year war.

A new truce has been hampered by rebel demands that the government pay wages for civil servants and even members of the armed forces in areas under Huthi control, including the capital Sanaa.

By attacking oil ports, Yemen's economic lifeline, the Huthis are "pressing for their demands to be met", Ahmed Nagi, a researcher at the Carnegie Middle East Center, told AFP.

The strikes also reveal the "economic challenges" facing rebels in territories they hold, as focus shifts from "power-sharing to sharing of resources", Nagi told AFP.

Revenues from oil exports totalled about $1.4 billion last year, according to the Central Bank of Yemen in government-controlled Aden.

The cash-strapped state produces around 80,000 barrels a day, according to government estimates, most of which is exported to finance the bulk of the government's budget.

Maged al-Madhaji, a researcher at the Sanaa Center for Strategic Studies, said the Huthi attacks amount to "blackmail" of the government.

"They want a share of resources without making concessions."

'Little to lose'

The Huthis seized Sanaa in 2014, prompting a Saudi-led coalition to intervene the following year to prop up the internationally recognised government.

Since then, the war has caused hundreds of thousands of deaths and pushed the impoverished nation to the brink of famine.

An estimated 24 million people -– nearly 80 percent of the population –- depend on humanitarian assistance to survive, according to the United Nations.

The recent port attacks, all claimed by the Huthis, "undermine peace efforts", Rashad al-Alimi, who heads Yemen's leadership council, said earlier this month.

Recognising their impact on Yemen's devastated economy, Alimi warned of "catastrophic humanitarian repercussions" if the government is unable to cover civil servant salaries and pay for public services.

In a briefing to the Security Council in November, UN envoy to Yemen Hans Grundberg called the Huthi attacks a worrying development.

These drone strikes deprive the Yemeni government "of its main source of revenue from exporting oil" and "undermine the welfare of the entirety of the Yemeni people", he said.

"They risk setting off a spiral of military and economic escalation."

Targeting ports is a "big gamble that risks pushing the government into an extreme" response, the researcher Madhaji warned.

Elisabeth Kendall of the University of Cambridge said the Huthis ultimately hold the advantage.

"While the Huthis may be militarily weaker than the coalition in absolute terms, they have little to lose and much to gain by continuing the fighting as they seek to win further concessions," the Yemen expert told AFP.

"The Huthis are essentially holding Yemeni oil ports to ransom."

Commenting on the truce, Kendall said: "there is still hope but it is fading fast."