Iran-backed Houthi militants seized the strategic port city of Mokha on Yemen's west coast Thursday, Yemeni and Saudi officials said, further expanding their control near the Bab al-Mandeb chokepoint for energy exports through the Red Sea.

The successful advance deepens the threat to Saudi oil exports at a time when Iran is crimping shipments through the strategic Strait of Hormuz on the other side of the Arabian Peninsula. Saudi Arabia had kept its exports up by piping crude across the desert to the Red Sea, but Houthi attacks have complicated that workaround.

The militants' seizure of Mokha-the early coffee trading hub and namesake of mocha-came after days of intense fighting with Saudi-backed Yemeni government forces in a conflict that has intensified since early July. Earlier this week, the Houthis struck Saudi Arabia's southern energy facilities and a military base with a large missile-and-drone attack that wounded dozens of people.

Houthi forces also began deploying on the Hanish Islands, which sit in the middle of the Red Sea just in from the strait, according to Yemeni and Saudi officials. Capturing the strategic islands would give the Houthis even more command of traffic in and out.

The escalating fighting in Yemen, the worst in the country in years, shows how the war in Iran is fueling instability throughout the Middle East and heightening the risk of further disruption to global energy flows after Iran's closure of the Strait of Hormuz caused the worst oil-supply disruption in recent history. It also drags Riyadh back into Yemen's civil war, a conflict it had tried hard to shake after a costly intervention beginning a decade ago that failed to dislodge the Houthis.

Saudi and Yemeni officials said the Houthis are now nearing complete control of the coast along the Bab al-Mandeb strait that links the Red Sea to big Saudi oil markets in Asia. Seizing Mokha gives them control of a major resupply hub for government forces, and further advances could cut off the main supply lines to government forces in the south, they said.

Tareq Saleh, vice chairman of Yemen's Presidential Leadership Council, reported casualties among government troops following days of relentless Houthi offensives.

Saleh said he ordered the establishment of a fallback command hub in a secure position to reorganize.

"It is a significant strategic setback for the Tareq Saleh-led National Resistance Forces and for the Saudi coalition," said Umer Karim, a researcher on Gulf security at the U.K.'s University of Birmingham. "Houthis are now advancing towards securing a foothold over the Bab al-Mandeb, which will exponentially increase their leverage over maritime traffic passing through the strait."

The Houthis are part of an array of militia groups throughout the Middle East that receive weapons and training from Iran and its Islamic Revolutionary Guard Corps as a part of Tehran's strategy to project power in the region. The group has grown closer with Iran in recent years but is seen as having more independence from Tehran than other militant groups like Lebanon's Hezbollah.

The Houthis had remained largely on the sidelines of the current war between the U.S. and Iran until a ceasefire in Yemen unraveled in July. Fighting escalated in the country after warplanes from the Saudi alliance bombed the international airport in the Yemeni capital to stop a plane carrying a delegation of Houthi officials returning from Iran from landing.

The Houthis retaliated by declaring a blockade of Saudi Arabia's nearby ports and began a series of attacks on shipping in the Bab al-Mandeb.

Yemen fell into a civil war after the Houthis stormed out of their northern strongholds to seize control of the capital, San'a, in 2014-a few years after a popular uprising that ejected a longtime autocrat from power during the 2011 Arab Spring.

Saudi Arabia intervened directly for more than half a decade. Since then it has backed Yemen's internationally recognized government and led the coalition of Arab militaries that supported its fight against the militants.

The civil war left the country effectively split into two states, with the Houthis in control of large areas of the north.