Yemen's city of Aden, a vital Arabian Sea port for centuries, is emerging as a key battleground in the fight between a Saudi-led Arab coalition backing the country's president and Shiite rebels and their allies.

The coalition is eyeing landing ground troops in the city to help secure a return of President Abed Rabbo Mansour Hadi, who was forced to flee the country by boat from the city this week. On Friday, heavy gunbattles raged in northern neighborhoods of the city between pro-Hadi militias and military units loyal to Hadi's predecessor, ousted autocrat Ali Abdullah Saleh, who is allied to the Shiite rebels known as Houthis.

Snipers of Saleh's forces were firing from rooftops, and bodies of fighters were seen in the streets, witnesses said. In a further sign of the chaos, looters were hauling away weapons from some bases in the city.

The city is largely a stronghold of supporters of Hadi, who hails from the south. His militiamen and soldiers hold the heart of the city, though they were in some disarray after Hadi's escape Wednesday and the capture by the Houthis of his defense minister. Hadi arrived Friday in Egypt for a weekend Arab summit.

Saleh's forces hold Aden's international airport and had two bases in the northern sections of the city, though they have largely abandoned those bases, fearing airstrikes. In a further complication, the district of Mansoura, also north of the city, is partially controlled by al-Qaida militants.

That makes any arrival by Arab troops a complicated mission. The heart of Aden is located on an extinct volcano off the coast, connected to the mainland by a narrow peninsula. The curve between the mountain and the coast forms a natural harbor where the port is located. The airport, held by Saleh's men, lies on the narrow peninsula, between the heart of the city and the northern neighborhoods on the mainland.

That port had been the source of the city's importance for centuries, as a way station for ships plying between the Middle East, Asia, Africa and Europe. Aden also lies 100 miles (120 kilometers) east down the coast from the vitally strategic Bab al-Mandab strait, the entrance to the Red Sea and from there to the Suez Canal. It's one of the world's busiest shipping lanes, a major route for oil from the Gulf and cargo between Europe and Asia.

Many Americans will remember Aden as the port where the USS Cole was bombed in an al-Qaida attack on Oct. 12, 2000, during a refueling stop. The explosion was carried out by suicide bombers in a small boat and killed 17 sailors.

Aden was colonized by the British for more than 100 years, leaving a legacy of colonial architecture in the neighborhoods ringing the slopes of the volcano rising out of the Arabian Sea waters. Old colonial villas are part of a presidential compound on rocks jutting out into the sea, used by Hadi in his last days in the city. The old Jewish school in the neighborhood of Crater, an ornate building that is now home to the city's tax department, testifies to the city's past when its minority Jewish community was at the heart of economic and commercial activity.

When the territory gained independence in 1967, Aden became the capital of South Yemen, distinct from the north. More than two decades of independence under a communist rule left secular traditions that southerners long felt distinguished them from the more tribal and religiously conservative north. Though Aden remains relatively liberal, those traditions have been eroded by an influx of northerners since reunification in 1990 and particularly since the north defeated the south in a 1994 attempt to regain independence.

The latest conflict in Yemen and worries about the security of Bab al-Mandab drove oil prices sharply up this week, but one expert said there was no major direct risk.

Yemen is a minor producer of oil and gas, and the disruption of its exports would not have much impact on global markets, said Richard Mallinson, geopolitical analyst at Energy Aspects research consultancy in London. The port is now closed because of the violence, but shipping that would sometimes use it for stopovers can find other options.

"I don't see much direct risk to shipping traffic in that strait," he said.

"The Houthis and other groups are focused on the intricacies of the domestic conflict," he said. "There isn't a group I can see where their primary aim would be to disrupt shipping and also have the ability to do it."

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Chang reported from Cairo. Hendawi spent a week in Aden on assignment earlier this month.