Renegade Congolese rebel leader Gen Laurent Nkunda has threatened to re-invade eastern Democratic Republic of Congo to bring "peace" to the area.
Nkunda accuses President Kabila of being dictatorial
In June last year he jeopardised DR Congo's shaky peace process when he briefly seized the town of Bukavu.
In a 17-page letter, extracts of which were published in the Congolese newspaper Le Potentiel, he accused the government of promoting ethnic hatred.
Meanwhile, the army has confirmed some of its men in the east have defected.
Correspondents in the area say an estimated 1,000 soldiers, who speak Kinyarwanda - the language spoken by the ethnic Banyamulenge whom Gen Nkunda claims to be fighting for - have gathered in Masisi, North Kivu province.
Gen Nkunda said he invaded Bukavu last year to protect the Banyamulenge from being targeted and killed by the Congolese army, but the UN dismissed his claims that he was preventing a genocide.
In his letter, seen by the BBC, Gen Nkunda said the transitional administration of President Joseph Kabila was corrupt and intent on promoting instability in the east.
He said the decision to stop more than 200,000 Congolese refugees living in neighbouring countries from returning home to Kivu to participate in the elections showed President Kabila's unwillingness to foster peace.
Elections were due before the end of June under the terms of the 2002 peace deal, but MPs have backed a six-month delay.
According to the BBC's Arnaud Zajtman in Kinshasa, the United Nations refugee agency has said it is not logistically feasible to organise the return of the refugees before the completion of the electoral registration process.
The UN mission in DR Congo has received a copy of the letter, but could not authenticate it, our correspondent says.
Gen Nkunda belonged to the Rwandan-backed RCD rebel group which fought the Kinshasa government in a five-year civil war
Under the peace deal, former rebel groups were supposed to be integrated into the new national army.
At the time of Bukavu's capture, President Kabila accused Rwanda of being behind the attack, but this was denied by Rwanda.
His ally, Col Jules Mutebutsi, has officially been granted refugee status in Rwanda after he and his men declared in writing that they had given up his armed struggle.
The Banyamulenge are ethnic Tutsis, who have lived in DR Congo for several generations but who retain ties to Rwanda.
An estimated three million people in DR Congo were killed during the five-year civil war, which drew in several neighbouring countries.