Yemeni government forces and their allies killed more than 800 al Qaeda fighters when they advanced into the port city of Mukalla, the Saudi-led pro-government coalition said.
Yemeni and Emirati soldiers seized the seaport on Sunday, depriving the group of the stronghold that has enabled it to amass a fortune during the country's civil war.
"In its first hours, the operation resulted in killing more than 800 members of al Qaeda and a number of their leaders while the rest fled," the coalition said in a statement carried by Saudi state news agency SPA late on Sunday.
Local Yemeni officials and residents said on Sunday that some 2,000 Yemeni and Emirati troops advanced into Mukalla, taking control of its maritime port and airport and setting up checkpoints throughout the southern coastal city.
They also said they had witnessed little fighting during the offensive.