(CNN) -- Separate blasts rocked the capital of Kenya on Monday, killing at least one person and injuring 20, officials said.
The second explosion took place at a crowded bus station in downtown Nairobi. One person was killed and eight wounded, according to the Kenyan police and Red Cross.
"This is a time when a lot of people would have been going home from work -- more or less rush hour," said Robert Nagil, a journalist in Nairobi.
Charles Owino, a deputy police spokesman, confirmed the explosion and said he was awaiting more details.
Initial reports say the blast killed one person and wounded eight, according to Carol Nduta, a spokeswoman for the Kenyan Red Cross.
The attack happened just two or three blocks from the site of a separate blast that injured 12 people at a nightclub earlier Monday.
"We have not yet linked attacks to anybody as we are still investigating," Owino said.
The explosions came two days after the U.S. Embassy in Kenya warned it had credible information of an imminent terror attack. The embassy did not offer details on who might carry out such an attack but said it had limited official U.S. government visits and urged citizens to consider deferring travel to Kenya.
The attack was likely to target places that foreigners congregate in Kenya, including malls and night clubs, the embassy said.
Kenya has been on edge since it sent troops across the border into Somalia to pursue militants with Al-Shabaab, an Islamist group that the United States and other countries consider a terrorist organization. Kenya sent troops into Somalia after the recent abductions of tourists and aid workers in Kenya. It blames the abductions on Al-Shabaab, which has denied involvement.
Al-Shabaab has threatened to attack Kenya if it does not withdraw its forces from Somalia.
Owino, the police spokesman, said the nightclub attack "could be Al-Shabaab or an individual. We are still investigating."
CNN's Jen Deaton contributed to this report