Ethiopian police have reportedly arrested 43 opposition members, for allegedly plotting against the government.
The May election was marked by protests
The official Ethiopian news agency reported the arrests took place in the central Amhara region.
The main opposition movement, the Coalition for Unity and Democracy, confirmed that a number of its branch offices had been raided.
The opposition is planning a large demonstration on Sunday.
The demonstration is intended as a protest against the results of May's general election, which the opposition says was rigged.
"The Amhara State Police Commission announced that it has arrested 43 [opposition] All Ethiopia Unity Party and Coalition for Unity and Democracy (AEUP-CUD) members allegedly found involved in violent activities aimed at subverting the constitutional order," the Ethiopian News Agency reported.
Prime Minister Meles Zenawi has said he will not allow anything to challenge the constitutional order, and accused the opposition of planning a "serious" crime.
Several days of violence followed the parliamentary elections and around 40 people were killed when police fired on protesters.