The United States, United Nations and Inter-Governmental Authority on Development (Igad) separately condemned Tuesday's attack on the Dusit Hotel complex in Nairobi.
A State Department spokesman described the attack as "a senseless act of violence," while UN Secretary-General Antonio Guterres denounced what he termed a "horrible terrorist attack."
The US Embassy is closely monitoring the incident and is working with Kenyan authorities to determine if there are any American citizens affected, the State Department spokesman said.
"We condemn this senseless act of violence," the spokesman said. "The US Embassy has actively offered assistance to local authorities."
Meanwhile, UN Secretary-General Antonio Guterres is condemning “the horrible terrorist act.”
Igad Executive Secretary, Amb Mahboub Maalim, described the attack as “cowardly and reprehensible.”
He also expressed Igad's “heartfelt condolences” to the families of the bereaved and wished quick recovery to those injured.
“At this moment of grief, I reaffirms Igad's solidarity with the people and Government of Kenya in their fight against terrorism and violent extremism,” Ambassador Maalim said in a statement on Wednesday.
Kenya's President Uhuru Kenyatta on Wednesday morning declared the terrorist attack at the 14 Riverside Drive over, with all the terrorists having been killed.
He did not specify the number of the gunmen that had stormed the DusitD2 Hotel and office complex in the leafy Nairobi neighbourhood of Westlands.
A total of 14 people were killed, the president said in an address broadcast on all major television networks.
Additional reporting by Joseph Oduha in Juba, South Sudan.