Ivory Coast President Laurent Gbagbo, has sacked three ministers from the former rebel group, the New Forces.
The opposition accuse Gbagbo of 'destabilising the peace process'
They were part of the power-sharing government set up last year as part of a deal to end a year-long civil war.
Ex-communications minister and rebel leader Guillaume Soro told AFP news agency the move "was tantamount to a coup d'etat against the peace accords".
The ministers were immediately replaced by members of Mr Gbagbo's Ivorian Popular Front party.
Diplomats say the crisis is plunging the country into one of its toughest periods since the war.
Earlier, President Laurent Gbagbo said he would suspend the salaries and restrict the freedom to travel of the rebels as punishment after they boycotted cabinet meetings.
The ex-rebels and the main opposition party, the Rally of the Republicans, withdrew from the cabinet after a banned opposition protest in the main city of
Abidjan was violently suppressed at the end of March.
The former ruling party - the Ivory Coast Democratic Party (PDCI) - had pulled out at the beginning of the month, accusing President Laurent Gbagbo of "destabilising the peace process".
Ivory Coast has been split since rebels seized control of the northern half of the country in September 2002.
Rebels hold the mainly Muslim north, while forces loyal to President Laurent Gbagbo control the south.
The conflict was declared over in January 2003, but the power-sharing "government of unity" outlined in the peace pact has never lived up to its name.