MOGADISHU, Somalia — A huge explosion from a truck bomb killed at least 20 people in Mogadishu, the police said on Saturday, and shaken residents called it the most powerful blast they have heard in years.

The explosion appeared to target a hotel on a busy road in the Hodan district and at least 15 people were injured, Capt. Mohamed Hussein said. Security forces had been trailing the truck after it raised suspicions, he said.

The Shabab, a Somalia-based extremist group, has recently stepped up attacks on army bases across the south and central parts of the country. While there was no immediate claim of responsibility for Saturday’s blast, the Shabab has often targeted high-profile areas of Mogadishu with deadly bombings.

Gunshots could be heard at the site of Saturday’s attack, and ambulance sirens wailed across the capital, which has been under tight security with military-staffed checkpoints.

David Concar, the British ambassador to Somalia, said in a Twitter post that the blast could be heard clearly from inside his country’s embassy. He posted videos from the rooftop showing a thick plume of black smoke rising in the distance.

The explosion left a trail of destruction across a busy intersection, with several bodies and bloodied slippers and shoes. Windows of nearby buildings were shattered. Overturned cars burned in the street. A large plume of smoke rose nearby.

The blast occurred two days after the head of the United States Africa Command was in Mogadishu to meet with Somalia’s president, and after the country’s defense minister and army chief resigned for undisclosed reasons.

The American military has stepped up drone strikes this year against the Shabab, an Al Qaeda-aligned group.