A suicide car bomber detonated a vehicle outside a presidential palace in southern Yemen, hours after the longtime vice president, Abd-Rabbu Mansour Hadi, was officially sworn-in as the country's new leader.

Security officials say at least 21 people were killed and several wounded in Saturday's bombing, which occurred in southern Hadramawt province, located about 400 kilometers southeast of the capital, Sana'a.

The bombing comes as a reminder of divisiveness Mr. Hadi will address as leader, with Yemen dealing with a separatists insurgency in the south, Shi'ite rebels in the north and an active wing of al-Qaida.

Mr. Hadi, who took his oath in front of parliament Saturday, pledged to continue the fight against the Islamist militant group (al-Qaida) and bring those displaced by Yemen's crisis back to their homes.

Mr. Hadi received more than 99 percent of the votes cast in this week's single-candidate presidential election, which will see him preside over a two-year transition period that envisions parliamentary elections, a new constitution and restructuring of the military. The handover cements a U.S. and Gulf-backed power transfer deal under which Mr. Saleh agreed to step down in return for immunity.

Mr. Saleh arrived back in Sana'a early Saturday after receiving medical treatment in the United States for injuries suffered during an assassination attempt. He is expected to formally hand over power during a ceremony at the presidential palace in Sana'a on Monday.