Kenya and Tanzania marked the 20th anniversary of the bombing of the US embassies in their countries.
The bombings were claimed by al-Qaida and killed more than 250 people. Hundreds of local survivors called on the US government for compensation.
The explosions occurred on August 7, 1998 and marked the first major al-Qaida attack on US targets. In total, nearly 5,000 people were injured.
Robert Godec, the US ambassador to Kenya, said the extremists had hoped to create a rift between the people of Kenya and the USA, but had failed.
"Their immediate purpose was to kill and destroy, but they had more in mind. They sought to divide us, to divide friends... to undermine the values we hold dear, to destroy civilisation itself and to replace it with a nightmare of oppression," Godec said.
In a separate statement, Secretary of State Mike Pompeo said, "Our partnership with our African allies remains stronger than ever."
One survivor of the Nairobi attack said hundreds of Kenyans were still pursuing compensation from the US, as American citizens working in the embassy had been compensated.
Douglas Sidialo, spokesman for the Kenyan victims' association, was blinded in the attack.
"You have to ask, do they care about the dreams and aspirations of the survivors? The unity the ambassador is talking about is a fallacy," Sidialo said.
The push to help Kenyan victims is now focused on the US Congress, Washington-based attorney Philip Musolino is representing some 538 victims with compensation claims.
According to AP, the embassy bombings brought al-Qaida to the attention of the US public and the world. This was three years before the September 11, 2001 attacks in New York and Washington that resulted in a death toll of nearly 3,000 people.
Kenya has remained under threat from the al-Qaida-linked al-Shabab group, which is based in neighbouring Somalia. The group claimed responsibility for the 2013 Westgate Mall attack in Kenya's capital, Nairobi which killed 67 people. Al-Shabab also claimed responsibility for the 2015 Garissa University attack, which killed 147 people, mostly students.
Al-Shabab has more recently been targeting Kenyan security forces. Nearly 100 police officers have been killed since May 2017 in bombings and ambushes.