Saudi forces clashed with Houthi rebels on the kingdom’s border with Yemen on Friday after a second night of Arab airstrikes in Sana’a, Yemen’s capital.

Egyptian and Saudi warships deployed to the Bab-el-Mandeb strait the same day to stop the Houthis taking control of the waterway. Forty kilometers wide at its narrowest, the strait sees large volumes of oil shipped through it every day bound for the Suez Canal.

Egyptian military and security officials told the Associated Press on Thursday a ground invasion of Yemen was imminent once bombardments had sufficiently weakened the Houthis as well as forces loyal to the country’s former strongman, Ali Abdullah Saleh.

A ten-country coalition of Arab states, led by Saudi Arabia, intervened in Yemen late on Wednesday at the request of the country’s internationally-recognized government. Its head, President Abd Rabbuh Mansur al-Hadi, fled to the port city of Aden in the southwest of Yemen when Houthi rebels from the north took over Sana’a and dissolved parliament in February.

The Saudis sees Iran’s hand in the crisis, accusing their regional rival of propping up the Houthi insurgents.

“We have to deal with Iran’s aggression in the region,” the kingdom’s ambassador to the United States, Adel al-Jubeir, told Fox News. “We’re dealing with their support of the Houthis and the Houthis’ attempt to take over in Yemen.”

The United States have backed the Saudi-led campaign with intelligence and logistical support. Western powers previously allied with Hadi against the Al Qaeda terrorist presence in Yemen. The group could take advantage of the chaos to strengthen its territorial control in the southeast where support for independence from the former North Yemen is also strongest.

The greater fear is that the war in Yemen will escalate the broader Iranian-Saudi standoff.

Iran has thrown its support behind the Houthi rebels who share its Shia faith. A delegation of Houthi leaders traveled to Tehran for talks earlier this month. Iranian medical supplies arrived in Yemen a day after the two regimes signed an aviation agreement. Reports that Iran has also supplied the Houthis with weapons are sketchy.

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.

The Financial Times reports that Saudi Arabia “appears to be betting that the Iranians will not intervene” in Yemen, “forcing the Houthis to the negotiating table.”

David Hearst, a veteran Middle East reporter, argued in The World Post on Thursday that Iran had overreached. “Could any ruler in Riyadh sit back and watch the leadership of millions of Sunni Arabs collapse in front of a coordinated advance of Iranian power — in Iraq, Syria and now Yemen?” he wondered.

If the kingdom had sat on its hands, it would have lost legitimacy in the eyes of its own citizens and pushed its youth into the clutches of the Islamic State.

According to Hearst, Saudi Arabia previously reached out to the Houthis, seeing them as a possible counterweight to Muslim Brotherhood Islamists in Yemen whom they regarded as the greater threat at the time. Those intrigues went wrong, however, when the Houthis took more control than they were supposed to.

That may at least in part have been because the rebels were tacitly support by Hadi’s predecessor and the Arab Gulf states’ former ally in Yemen — Saleh.

The Financial Times argues that the Houthis’ vertiginous ascent of the past two years was unlikely to have succeeded without the former strongman.

When the rebels sliced through Amran, a tribal stronghold of conservative Sunnis who previously fought the Houthis, it was with the backing of tribes loyal to Mr Saleh. And when the Houthis arrived in Sana’a last September, they did so with the support of military units loyal to the Saleh family.

Saleh, who presided over Yemen’s unification in 1990 and a civil war that started in 1994 when the south tried to secede, was forced out of office by his Arab Gulf neighbors in 2012 amid fears of an “Arab Spring”-style uprising in the impoverished Arab country.

The Arab intervention in Yemen may be inopportune for American president Barack Obama who hopes to secure a nuclear agreement with Iran in the coming days.

Egypt and Saudi Arabia worry that their ally will acquiesce in recent Iranian strategic gains in the Middle East — notably in Iraq where Tehran supports the Baghdad government’s fight against Islamic State jihadists — under an agreement to stop Iran from obtaining nuclear weapons.