A well-known Congolese opposition leader was arrested by military officers at his party's headquarters in the capital Kinshasa on Sunday, witnesses said.
The arrest of Mr Martin Fayulu, president of the Engagement for Citizenship and Development party (Ecide), comes just two days before a general strike called by opponents of President Joseph Kabila.
Mr Fayulu's small Ecide party is among the organisers of the nationwide February 16 strike.
Eyewitnesses, including party members, told AFP that Mr Fayulu was taken to an unknown destination by a group of men in military and civilian clothing.
The men appeared to be led by an officer from the Democratic Republic of Congo's DEMIAP military intelligence agency, which investigates unpatriotic acts, they said.
Political tension has been on the rise in the DR Congo ahead of a presidential vote due at the end of the year, which Mr Kabila, who has been in office since 2001, cannot contest under the current constitution.
Mr Kabila last November called for a "national dialogue" to help ensure "peaceful elections", but the opposition accuses the president of seeking to delay the polls in order to find a way to get around the constitution and cling to power.
The United Nations as well as a number of rights groups have voiced concern in recent months at what they say is a growing crackdown on Mr Kabila's critics.