According to the Aden governor, Aidarous al-Zubaidi, the curfew will be in place every night from 8 p.M. To 5 a.M. For an unspecified period.
The measure came after government forces retook Aden's strategic port after heavy clashes with militants who had seized it earlier over the weekend. Al-Qaida and other militants have been using the port for lucrative smuggling operations.
Yemen's al-Qaida branch has long been seen by Washington as the most potent affiliate of the extremist network and has been linked to a number of attempted attacks on the US.
The group, known as the Al-Qaida in the Arabian Peninsula, has captured much of Yemen's sprawling Hadramawt province and its capital, Mukalla, as well as the capital of southern Abyan province, Zinjibar and the town of Jaar.
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According to UN figures, the war in Yemen has killed at least 5,884 people since March, when fighting escalated after the Saudi-led coalition began launching airstrikes targeting the rebels.
The conflict pits the internationally recognized government, backed by a Saudi-led coalition against the Shiite Houthi rebels, allied with a former president.
The two sides launched peace negotiations in December in Switzerland, and a truce was declared on the ground, which never really took hold as both the government forces and the rebels ignored it. That truce formally ended over the weekend.
Saudi Arabia's UN Ambassador Abdallah al-Moualimi said his country's ruptured diplomatic ties with Iran will have no effect on its efforts to promote peace in Yemen.
"We hope that the talks will be productive," he told reporters at UN headquarters in New York.
"That pretty much depends to a great extent on the behavior of the Houthis."
Al-Moualimi said the "critical element" is whether the Houthis implement a Security Council resolution adopted in April 2015 demanding that they withdraw from areas they have seized including the capital of Sanaa, relinquish arms and missiles seized from military and security institutions, and release all political prisoners.