According to witnesses, a small car drove into other vehicles leaving the Medina Hotel in Belet Weyne -- a city about 250 miles north of the capital Mogadishu -- and exploded.
Information Minister Farhan Ali Mohamud announced Aden's death but gave no further details, the Associated Press reported.
Somalia's President Sheik Sharif Sheik Ahmed accused al-Qaida of being behind the bombing but did not offer any evidence. "It was an act of terrorism and it is part of the terrorist attack on our people," he told reporters in Mogadishu. "Al-Qaida is attacking us."
He said the attack also killed a senior Somali diplomat. The death toll came from officials and hospital sources.
Al-Shabab spokesman Ali Mohamud Rage told local radio stations by phone that his group carried out the attack and that one of their fighters died.
"We killed the national security minister and the former ambassador to Ethiopia," said Rage, speaking from an undisclosed location, reported the AP.
Al-Shabab, an extremist Somali Islamic group, is considered by the U.S. State Department to be a terrorist organization with links to al-Qaida, though al-Shabab has denied those links.
The insurgent group is one of several trying to topple the U.N.-backed government for three years. Al-Shabab stepped up attacks in early May to try to oust the president, and clashes have killed about 300 people since then, according to Reuters.
On Wednesday, at least 10 people died when a mortar hit a Mogadishu mosque, the BBC reported. The city's police chief was killed in a separate attack.
Somalia has not had an effective government for 18 years after warlords overthrew a longtime dictator and plunged the country into chaos. The lawlessness also has allowed piracy to thrive off the country's coast.
