The blast happened hours after Abd Rabbu Mansour Hadi was sworn as Yemen's new president [Reuters]

A car bomb has caused many casualties and injuries outside a presidential palace in southern Yemen on the day that the country swore in a new president.

Health officials told news agencies that at least 25 people were killed and 30 injured in the attack in Mukalla, the capital of the southeastern Hadramaut province on Saturday. All of those killed were soldiers in the Yemeni Republican Guard, which serves as the presidential security force.

"A pick-up truck driven by a suicide bomber exploded at the entrance of the presidential palace in Mukalla," an official said.

Reuters news agency reports that al-Qaeda has claimed responsibility for the bombing, "in retaliation for the Republican Guard's crimes".

However, Al Jazeera's Hashem Ahelbarra, reporting from the Yemeni capital of Sanaa, said that while the attack "bear the fingerprints of al-Qaeda" there is no confirmation yet that the group is responsible for the killings.

"Al-Qaeda has launched its first attack (in Mukalla) in 2002, when it attacked a French oil tanker ... bringing more international scrutiny of al-Qaeda activities in the eastern part of Yemen," said Ahelbarra.

"However, it's also an area where the separatists of the south are also very active."

The attack came hours after Abd-Rabbu Mansour Hadi was sworn in as Yemen's new president after being declared the winner of last week's single candidate vote, completing a transition of power that formally ended Ali Abdullah Saleh's decades-long rule.

Our correspondent said that Saturday's attack "stresses the challenges that the new president will have to face in the future."

Hadi, who served as vice president under Saleh, took the oath of office at a ceremony in Sanaa on Saturday attended by his predecessor, who returned to the country from the US for the occasion.

Yemen has been rocked by months of deadly unrest since protests against Saleh's rule began early last year.