Shiite militiamen who seized power in Yemen vowed to defy "threats" as the UN Security Council prepared to adopt a resolution Sunday calling on them to step aside or face consequences.

Yemen is a traditional US ally in the fight against Al-Qaeda, but the impoverished Arabian Peninsula country has descended into chaos since the militia known as Huthis overran the capital in September.

In another city they captured last year, Ibb in central Yemen, Huthis fired on hundreds of protesters to disperse them on Sunday, wounding several.

Following their seizure of Sanaa and Ibb, the crisis deepened when they ousted the government and dissolved parliament on February 6, tightening their grip after Western-backed President Abedrabbo Mansour Hadi resigned in protest at their advance.

UN Secretary General Ban Ki-moon has warned that Yemen is falling apart and called for Hadi's reinstatement.

Citing security concerns, nine Arab and Western countries shuttered their embassies in Yemen last week and evacuated diplomats.

The Security Council is expected to adopt a resolution calling on the militia to withdraw its forces from government and security institutions "immediately and unconditionally".

It also urges the Huthis to "engage in good faith in the UN-brokered negotiations" led by special envoy Jamal Benomar and to release Hadi, his Prime Minister Khalid Bahah, and other officials and activists under de facto house arrest or in detention.

According to Western diplomats, Russia, which is already under US and European sanctions over its annexation of Crimea and backing of rebels in eastern Ukraine, was reluctant to vote for sanctions.

The text marks the Security Council's first resolution on Yemen since the Huthis ousted the government and parliament, in a move the United States and Gulf Arab countries have described as a "coup".

At a Riyadh meeting of the Gulf Cooperation Council on Saturday, Yemen's neighbours urged the UN to evoke Chapter Seven of the United Nations Charter, which allows for economic and military pressure to enforce Council decisions.

They said they themselves would act if the rival factions fail to resolve their differences, without elaborating.

The 57-member Organisation of Islamic Cooperation (OIC) voiced support Sunday for the GCC statement and condemned the Huthi "coup".

And the Arab League said it will hold an emergency meeting on Yemen on Wednesday.

Huthi spokesman Mohammed Abdulsalam, quoted by the official Saba news agency which the militia controls, insisted that "the Yemeni people won't cede power in the face of threats".

Abdulsalam said Yemenis were "engaged in a process of self-determination free of any (foreign) tutelage".

He denounced as "provocative blackmail" demands for the Huthis to relinquish power and criticised the withdrawal of ambassadors.

In their bid to establish authority across Yemen, the militiamen have tried to stifle opposition and have been accused of detaining and torturing opponents.

They announced a ban on anti-Huthi protests last week and have repeatedly used live ammunition to disperse demonstrations in Sanaa and Ibb.

The family of one protester detained by the Huthis last week said he had died late Friday of torture wounds suffered in captivity.

Another two demonstrators who were held with him have been hospitalised after being found wounded and left on a street.

On Sunday, several protesters were wounded in Ibb when the Huthis fired live rounds to disperse hundreds of people demanding the release of an activist, witnesses said.

Ahmed Hazzaa, a leader of the anti-Huthi Rafdh (rejection) Movement, was detained on Saturday in Ibb by Shiite militiamen, members of his group told AFP.

The Huthis are accused of receiving support from Shiite-dominated Iran which criticised the "hasty action" of closing embassies in Sanaa, and insisted the Huthis were fighting "corruption and terrorism".

Meanwhile political forces and governors of three southern provinces -- Aden, Lahij, and Mahra -- formed a local "administrative, security, and political leadership rejecting the coup" by the Huthis.

In a statement issued at the end of a meeting in the main city of the south, Aden, leaders of the three provinces rejected all decisions by the Huthis, called for Hadi's reinstatement and affirmed their support for Yemen becoming a federation based on the outcome of a national dialogue held last year.