NAIROBI, Kenya — The death toll from an extremist attack on a luxury hotel and shopping complex in Nairobi climbed to 21, police said Wednesday in the aftermath of the brazen overnight siege by al-Shabab gunmen.

Five militants were killed and two people accused of facilitating the attack were arrested.

The number of those killed at the DusitD2 complex rose with the discovery of six more bodies at the scene and the death of a wounded police officer, said Joseph Boinnet, inspector-general of Kenyan police. Twenty-eight people were injured and taken to the hospital, he said.

In a televised address to the nation earlier in the day, President Uhuru Kenyatta announced that the all-night operation by security forces to retake the complex was over and that all of the extremists had been killed.

“We will seek out every person that was involved in the funding, planning and execution of this heinous act,” he said.

In an attack that demonstrated al-Shabab’s continued ability to strike Kenya’s capital despite setbacks on the battlefield, extremists stormed the place with guns and explosives. Security camera footage released to local media showed a suicide bomber blowing himself up in a grassy area in the complex, the flash visible along with smoke billowing from the spot where he had been standing.

Of the civilian victims, 16 were Kenyan, one was British, one was American and three were of African descent but their nationalities were not yet identified, police said.

The American killed was identified as Jason Spindler, co-founder and managing director of San Francisco-based I-DEV International. Spindler’s father, Joseph, said his son worked with international companies to form business partnerships in Kenya that would boost local economies.

The Houston-raised Spindler had a brush with tragedy on 9/11: He was employed by a financial firm at the World Trade Center at the time of the 2001 terrorist attack but was running late that morning and was emerging from the subway when the first tower fell, his mother said.

He became covered in dust and debris as he tried to help others, Sarah Spindler told KTRK-TV in Houston.

Al-Shabab, based in neighboring Somalia and allied with al-Qaida, claimed responsibility.

The Islamic extremist group also carried out the 2013 attack at Nairobi’s nearby Westgate Mall that killed 67 people, and an assault on Kenya’s Garissa University in 2015 that claimed 147 lives, mostly students.