The conflicting statements came as peace talks scheduled to resume in Doha last week have been delayed. In the declaration of principles, Congo and M23 pledged to begin talks by August 8 and aim for a final deal by August 18.
Neither side currently has delegations in Doha.
M23 leader Bertrand Bisimwa said last week that the rebels had not received an invitation to the talks.
The earlier M23 statement said Congo’s army had carried out significant troop movements and military equipment deployments in six different locations.
The Qatar-hosted talks were intended to run parallel to a mediation effort by U.S. President Donald Trump’s administration involving Congo and Rwanda.
Washington hopes the diplomatic push will produce a sustainable peace and attract billions of dollars of Western investment to a region rich in tantalum, gold, cobalt, copper, and lithium.
M23 rebels seized eastern Congo’s largest city, Goma, in January as part of a rapid advance that has given them control of more territory than ever before.