affirm, assert, allege, claim, announce, proclaim这一组动词都有“声称”的意思。

affirm v.坚信不疑地肯定或宣称，是deny的反义词。

He affirmed his love for her.
他发誓爱她。

assert v.指不管事实如何，主观自信地宣称，或者清楚有力地坚持某个情况为事实。

She asserted that she was innocent.
她宣称自己是无辜的。

allege v.在无真凭实据的情况下宣称、断定。

The suspect alleged that he had not been in the neighborhood at the time of the crime.
嫌疑犯声称案发时他不在现场。

claim v.要求，声称，断言。多指根据某种规定提出的要求或主张。

They claim that if more people rode bicycles to go to work there would be fewer automobiles in the downtown section of the city.
他们生成如果有更多的人骑自行车上班的话，闹市区的汽车就会有所减少。

announce v.宣布，宣告。多指首次当众正式宣布某一主张或态度，常常带有预告的意味。

The invention of the printing press announced the diffusion of knowledge.
印刷术的发明宣告了知识普及时代的来临。

proclaim v.宣布；宣告(成立)。指经过深思熟虑后向大众宣布一个明确的决定或判断，尤其指重大事件的宣布，多用于官方场合。

The president proclaimed an emergency when the war came.
当战争来临的时候总统宣布进入紧急状态。