Warships shelled Houthi fighters and troops loyal to former Yemeni strongman Ali Abdullah Saleh as they advanced on the southern port city of Aden on Monday, the news agency Reuters reported.

The vessels, likely Egyptian, were the first navy units taking part in the conflict since Saudi Arabia launched airstrikes against opponents of Yemen’s internationally-recognized president, Abd Rabbuh Mansur al-Hadi, late on Wednesday.

Egyptian military and security officials told the Associated Press last week that a ground invasion of Yemen was imminent once bombardments had sufficiently weakened the Houthis and Saleh loyalists. Egyptian and Saudi warships deployed to the Bab-el-Mandeb strait the following day to prevent the waterway from falling under rebel control.

Forty kilometers wide at its narrowest, the strait sees large volumes of oil shipped through it every day bound for the Suez Canal.

A ground assault would be risky and may not be necessary if the airstrikes succeed in driving a wedge between the Houthis and Saleh’s forces who, the Financial Times reported last week, allowed them to slice through Amran — a tribal stronghold of conservative Sunnis who previously fought the Houthis — and storm the capital, Sana’a, in September. The bombardments could stop the Shia rebel group taking over the area around Aden which is Hadi’s last stronghold, argues Bilal Y. Saab, a Middle East expert at the Atlantic Council, in Foreign Affairs magazine, and compel them “to come to the table for peace talks with the elected government and other Yemeni factions.”

Saleh, Hadi’s predecessor, presided over Yemen’s unification in 1990 and the civil war that started in 1994 when the south tried to secede. He was forced out of office by his Arab Gulf neighbors in 2012 amid fears of an “Arab Spring”-style uprising in the impoverished Arab state but still leads Yemen’s ruling party and commands the loyalty of army commanders. His alliance with the Houthis appears to be one of convenience.

Despite Iranian support for the Houthis and Saudi fears of Iranian encirclement, the Houthi revolt is primarily a local affair, writes Adam Baron, a visiting fellow at the European Council on Foreign Relations, for Al Jazeera.

It was spurred by the deterioration of central government control before Saleh’s exit and then exacerbated by his successor’s inability to consolidate power — all of which created a perfect opening for the Houthis whose complaints about corruption and widespread pernicious foreign influence seemed to resonate with more Yemenis than ever.

Until the middle of last year, the Houthi campaign was little more than a turf war against tribal opponents in the highlands of northern Yemen. Only recently, with the support of Saleh loyalists, did they take the fight to the central government.

Baron cautions against portraying the conflict in Yemen as a proxy war between Iran and Saudi Arabia. “Regardless of their veracity,” he argues, “such framings risk becoming self-fulfilling prophesies.”

Saudi Arabia’s priority, according to Saab, is nevertheless to safeguard the country “from what Riyadh perceives as an immediate military threat posed by advancing pro-Iranian Houthi rebels.”

Iran and Saudi Arabia are locked in a struggle for hegemony in the Middle East. The powers back opposing sides in Syria’s civil war. Iran supports the regime of President Bashar al-Assad while Saudi Arabia has armed and financed the largely Sunni uprising against him.

Should the Saudi-led intervention fail, Saab warns it could embolden Iran and encourage it to continue its expansionist policies Iraq and the Levant.