A consensus appears to be building in Riyadh, Cairo, and Islamabad toward inserting ground troops into the conflict in Yemen.

One Egyptian military official told BuzzFeed News the decision had already been made. "Ground forces will enter the war," the official said on condition of anonymity in order to discuss classified military operations.

The timing of such a move, which would be a significant escalation in the Saudi-led air campaign in Yemen, is still being discussed. But the Egyptian military source said it could happen as soon as "two or three days."

There has been no official comment from the Egyptian government on sending troops or the size of any potential operation. Youssef al-Sharqawy, Egypt's Ambassador to Yemen, however, refused to rule out ground troops in an interview with al-Monitor on Tuesday.

Two weeks of Saudi airstrikes have failed to halt the advances of the Huthis, a Zaydi-Shi'a group that has taken over large parts of the country. Saudi Arabia, which sees itself locked in a battle with Iran for control of the region, is portraying the Huthis as an Iranian proxy.

Days of bombings have destroyed much of Yemen's military infrastructure, including weapons depots and heavy equipment, which the Huthis could have used to resist ground forces.

Egyptian President Abdel Fattah al-Sisi held a six-hour meeting focused on Yemen with the Supreme Council of the Armed Forces on Saturday. According to Article 152 of Egypt's Constitution, Sisi must consult with the Supreme Council before dispatching ground troops outside of Egypt, a stipulation he does not need to use air power. The same article also requires Sisi to obtain the "approval of both the cabinet and the National Defense Council."

On Monday, Sisi dispatched his defense minister, Sedki Sobhi, to Pakistan for consultations. That same day, Pakistan's defense minister informed parliament that Saudi Arabia had requested military hardware and additional soldiers for the war in Yemen. And on Tuesday, Anthony Blinken, the U.S. deputy secretary of state, told reporters in Riyadh that the U.S. had "expedited weapons deliveries," while also increasing "intelligence sharing."

Iran, which has done little militarily during the air strikes, responded to these latest moves by dispatching a navy destroyer to waters off Yemen's coast, according to reports by the Associated Press.

The Saudis stated goal is to restore Abdu Rabu Mansur Hadi, Yemen's internationally recognized president, to power. But Hadi, who is currently in Riyadh after fleeing Yemen, has little real support on the ground, and is unlikely to be able to be welcomed back after calling for airstrikes on his country while abroad. In the absence of other options, U.S. diplomats continue to consult with Hadi in Riyadh.

Although the past few days suggest that the 10-country coalition led by Saudi Arabia is ready to dispatch ground forces, it is less clear what those troops would do in Yemen, how effective they could be, and even where they would be able to enter the country.

Aden, a port city in southern Yemen, is an obvious candidate. But the city lacks what one Yemeni official called a "green zone," a place for troops to land. "They would have to fight their way in," the official told BuzzFeed News.

Even without an influx of foreign troops, Yemen's second largest city has been battered by days of heavy fighting and nightly aerial bombardments. The Huthis and troops loyal to former Yemeni president Ali Abdullah Salih are struggling to take control of the city from a series of local militias, some of whom have called for secession, and handfuls of citizens looking to protect their property. Water and have been cut periodically, and severe fuel shortages have made it difficult to transport the wounded to hospitals.

The World Health Organization estimates that at least 643 people have died in the fighting, although this number is likely to rise as additional casualties are reported and verified.

Writing in the Guardian on Monday, Valerie Pierre, a coordinator for the NGO Doctors Without Borders in Aden, described the scene in her neighborhood. "There are fighters everywhere and we don't know who is controlling the area outside the hospital — it seems to change on an hourly basis."

Hundreds of miles north, Saudi Arabia has also moved equipment and troops, including Pakistani soldiers, near its southern border with Yemen in advance of a possible ground invasion. But the territory in the north, particularly in Sadah where the Huthis are based, is much more rugged with steep mountains and deep valleys. The Huthis have already fought and survived six wars over the past decade across topography that often puts conventional troops at a disadvantage against hardened guerrilla fighters.

Another possible insertion point could be Yemen's lengthy southern coast. But al-Mukalla, another major port city, is currently under the control of Yemen's al-Qaeda branch. Yemen's western coast along the Red Sea presents similar problems.

Along with the militias in the south, there are also tribes in Marib, a desert province east of the capital of Sanaa, who might form natural allies. But these tribes tend to be more anti-Huthi than they are pro-Saudi.

Indeed, much of Saudi Arabia's history of intervention in Yemen would seem to argue against a quick or easy resolution to what is rapidly becoming an ugly war. In 2009, the Saudis were embarrassed by the Huthis in a series of border skirmishes. And in the 1960s, both Saudi Arabia and Egypt intervened — on opposite sides — in a palace coup turned civil war that dragged on for eight years, sucking up men and money.

Egypt's Sisi dismissed those sort of historical comparisons, telling reporters in Cairo: "Our intervention then and the existing reality now are very different." But while Egypt may have changed, Yemen's geography and its tribes have not.

The war in the 1960s remained in Yemen. There is no guarantee that this one will do the same, particularly as all sides play on sectarian tensions in their efforts to demonize the other.