Congolese President Felix Tshisekedi will launch a unity government, his spokesperson said on Saturday, as he faces domestic pressure over his handling of an offensive by Rwanda-backed M23 rebels in eastern provinces.

The M23's capture of swathes of eastern Congo and valuable mineral deposits has fanned fears of a wider war and provoked some members of the fractious opposition to openly predict his presidency will not last.

On Saturday, Tshisekedi told a meeting of the ruling Sacred Union coalition not to be distracted by internal quarrels: "We must unite ... let's stand together to face the enemy."

Presidency spokesperson Tina Salama said Tshisekedi would form a government of national unity and make changes in the leadership of the coalition, without giving further details.

Since the start of the year, Congo has faced back-to-back losses in North and South Kivu provinces, fueling criticism of the authorities' military strategy.

"Tshisekedi is more concerned with saving his power, whereas we are more concerned with saving the Congo, and this can be done with or without him."