The attack on the dusitD2 hotel began shortly after 3pm with an explosion in the parking lot and then a suicide bombing in the foyer, police said. Somali militant Islamist group al-Shabaab claimed responsibility for the attack.
In an addition to the American victim, eleven Kenyans and a Briton were among the casualties, local officials said. No Israelis were reported to have been hurt in the attack.
The American victim, Jason Spindler, was the head of a consulting firm with offices located in the hotel complex that was attacked, according to the Washington Post. Spindler was attending a work meeting when he was fatally shot by the terrorists. His family was notified of his death and are making their way to Kenya. Spindler graduated the law school of New York University and had previously volunteered for the Peace Corps.
Spindler's friends have contacted the American embassy and the head of the Jewish community in Nairobi, Rabbi Silverstein, regarding the repatriation of his body back to the United States.
Sarah Spindler, Jason's mother, said her son worked toward making a positive change in the developing countries. “We miss him so much and it's extremely sad that such a positive young man was taken away from us by the terrorists," she said.
His close friend, Chris Schroder, paid tribute on Twitter to Spindler as “one of those rare men who was loved by pretty much anyone be touched in Kenya and around the world."
He added: "Today he was killed in the terrible al shabab attack in Nairobi. He chose a life of hope and inclusion. I am grateful to have known and learned from him.”
At least two groups of people remained trapped inside the hotel until early Wednesday morning as the security forces surrounded the complex. Later, Kenya's President Uhuru Kenyatta confirmed that security forces had killed all militants involved in the attack. "All the terrorists have been eliminated," said Kenyatta.
In a televised address, Kenyatta did not confirm the earlier reports that four gunmen were involved in the attack. He said more than 700 people were evacuated during the security operation and he urged Kenyans to "go back to work without fear," saying the East African country is safe for citizens and visitors.
Associated Press contributed to this report