SANAA (AP) ― The death toll of an al-Qaida suspected attack on a Yemeni intelligence headquarters rose to 20 on Saturday, in the worst such attack in a year that highlights the challenges faced by the country’s new leadership as it struggles to bring security and reconcile a military with split loyalties.

The attack, in the heart of the port city of Aden, underscored al-Qaida’s ability to launch deadly strikes despite a two-month Yemeni military offensive backed by the U.S. that earlier this year dislodged militants who had taken over a string of southern towns near Aden.

In a coordinated attack, two groups of masked militants stormed the intelligence building from two sides, firing automatic weapons and rocket-propelled grenades, according to intelligence officials in the city and witnesses from the adjacent state TV and radio building.

While one group clashed with guards of the intelligence building’s main gate, a second threw a bomb at a small mosque, killing soldiers who were resting and sleeping inside, officials said. The gunmen then sprayed their victims with bullets before detonating a car bomb in front of the intelligence building, collapsing its facade.