Yemenis in the port city of Aden have been awaiting the arrival of Houthi rebels for weeks. Since the deposed Yemeni President Abd Rabbuh Mansur Hadi fled the country after establishing a government in exile in that city, it’s fall to the Shiite-dominated rebel group has appeared imminent.

The fighting overnight has been intense. “Witnesses have reported bodies lying in the street after intense rebel shelling and sniper attacks,” BBC reported. “A spokeswoman for the aid agency Medecins Sans Frontieres (MSF) told the BBC that its hospital in Aden had received more than 500 injured people from all sides in the conflict over the last two weeks.”

“Shiite rebel forces backed by tanks and heavy machine guns pushed deeper into Yemen’s second-largest city on Wednesday in a bid to strengthen their hold even as Saudi-led airstrikes attempt to cut off their supply lines and cripple their capabilities,” A Washington Post dispatch revealed.

The showdown over Aden, a key port and gateway to Yemen’s south, underscores the imperatives on both sides in the widening conflict — in which Saudi Arabia and its Arab allies have launched a campaign to beat back the rebels, thought to be backed by Shiite power Iran, and block a perceived bid by Tehran to expand its influence.

The rebels, who control Yemen’s capital, Sanaa, hope to find new defensive positions and open fresh supply channels by taking full control of Aden. The Saudi-led alliance, meanwhile, is trying to hang on to the city but is wary about carrying out airstrikes in populated areas for fear of civilian casualties.

And the chaos in Yemen is not limited to Aden or Sanaa. In the neighboring port city of Mukalla, al-Qaeda militants reportedly stormed a local prison and set 270 detainees free.

“Khaled Batarfi, a senior al Qaeda figure, was among the escapees, officials said,” CNN revealed. Batarfi had been a senior leader of AQAP in Yemen and a member of the group’s governing Shura council until his 2011 arrest.

The rebel advance continued this morning, and it has yielded spectacular gains:

The air war led by Saudi forces and including the air forces of a number of Arab region nations is apparently evolving, and the long-anticipated ground invasion of Yemen may have begun on Thursday. Early Thursday morning, reports began to indicate that “dozens of troops” have begun to disembark at the port of Aden. The nationality of those troops has been described by port officials as “unknown,” but conflicting dispatches from the region suggest that the troops were either Saudi or Egyptian in origin.

There are others, however, who suggest that these reports were false, and that the suspicious troops are merely more of those who are loyal to the Houthis and former Yemeni President Ali Abdullah Saleh.

It seems as though the ground invasion excitement is now over even before it fully took off. According to a report from reporters with Lebanon’s The Daily Star, reports of foreign ground troops in Aden were wildly exaggerated.

“Yemen says armed guards were confused for ground troops at Aden port,” The Star reported.

When long-awaited invasion occurs, if it occurs, it won’t stop with a few dozen troops landing in Aden. The operation would likely be accompanied by a major influx of fighters by sea into Aden and across the Saudi border to the North. If this is the operation to roll back the Houthi tide, it might start with a trickle, but it will end in a flood.