Shiite rebels who breezed into the Yemeni capital unopposed last month are now widely thought to be moving to cement their grip by snatching a strategic strait and oilfields.
The militiamen known as Huthis stormed into Sanaa on September 21, easily seizing key government installations, and they now man checkpoints and run patrols across the city in almost total absence of the security forces.
The rebels, who Yemeni authorities accuse Shiite-ruled Iran of backing, have refused to quit Sanaa despite a UN-brokered deal to give them more influence with the Sunni-dominated government.
Numerous sources in Yemen say the Huthis are now setting their sights on prized assets like the narrow Bab al-Mandeb strait leading to the Suez canal, as well as oilfields in Marib province.
Bab al-Mandeb, a chokepoint whose Arabian shores are only 40 kilometres (25 miles) across the water from Africa, carried an estimated 3.4 million barrels of oil a day in 2011, according to US Energy Information Administration.
But first, the rebels who fought the central government for more than a decade are looking to take control of the nearby export terminal of Hudeida on the Red Sea, where they opened an office last week.
"Hudeida is the first step before they extend their presence through the Popular Committees throughout the coastal strip to Bab al-Mandeb," a military official told AFP, requesting anonymity.
Another military official said the aim of the Huthis was to "control Bab al-Mandeb, as well as Dhubab and Makha -- two coastal regions that represent a passage for all sorts of smuggling, including arms."
The rebels, who are also known as Ansarullah, already had thousands of armed men in Hudeida, the official added.
Acting under the guise of the so-called "Popular Committees," the rebels are attempting to oversee public finances through "systematic control" of the finance ministry and central bank, according to employees.
The rebels have also set up a parallel justice system through a "complaints office" that resembles an Islamic law court, headed by Abdulkarim Emireddine Badreddine al-Huthi, the nephew of Ansarullah leader Abdulmalik al-Huthi, a local official said.
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- Eyes on oil -
In the east of the country, the rebels are apparently eyeing Yemen's oil and gas reserves in Marib.
"They are looking to venture into the province of Marib, hoping that with the aid of allied tribes they could control the oil and gas wealth, as well as the main power plant that feeds the capital," said a source close to the rebels.
"But this plan faces resistance from tribes hostile to the Huthis, mainly the Abida and Murad tribes, who have mobilised their armed men," according to a tribal chief.
He pointed out that the Abida and Murad were allies of tribes that fought the rebels during the past three months in Jawf province, north of Marib.
And by stretching their presence to Marib, the rebels risk provoking a fight with Al-Qaeda militants, who are active in the mostly desert province, as well as southern regions, political sources said.
The rebels' leader suggested this potential confrontation in a weekend statement on the occasion of the Muslim festival of Eid al-Adha, in which he condemned "plots against some provinces, including southeastern Hadramawt".
Hadramawt is a stronghold of Al-Qaeda in the Arabian Peninsula, or AQAP, which the United States considers the jihadist network's most dangerous affiliate.
The Huthis, who complain of marginalisation since the rule of now-toppled autocrat Ali Abdullah Saleh in 2011, are concentrated in the rugged northwestern mountains where Shiites are a majority in otherwise Sunni-majority Yemen.
Building on their seizure of the capital, they are said to be trying to infiltrate the security forces by insisting on enrolling their men in the army and police force.
"The Huthis are negotiating the integration of some 20,000 of their fighters into the army, security forces and intelligence services," said a security official.
The developments have added to the instability in Yemen since the bloody uprising that ousted Saleh.
But they also threaten an already volatile region, with the Sunni-dominated Gulf Cooperation Council saying on October 1 that it "will not stand idly by in the face of factional foreign intervention," in reference to Iran's alleged backing for the Huthis.