Officials from the party of Democratic Republic of Congo's former President Joseph Kabila appeared before a military prosecutor on Monday in a sign of political tensions over advances by Rwanda-backed rebels in the east.

The exact reason for the invitation to appear before the prosecutor was not clear, said Jean Mbuyu, a lawyer for the officials and former security adviser to Kabila.

But after leaving the prosecutor's office on Monday evening, one of the officials told Reuters they had been called in for questioning over February 26 comments made by Aubin Minaku, vice president of the party and former president of the National Assembly.

"The chief said 'we must be ready for anything'," Minaku said at the time, referring to Kabila.

"When the chief says we must be ready for everything, each of us, a pure-blooded (party member) understands... the time for silence, for clandestine actions is over, now is the time for open actions."

Marcel Bombamba, another of the group's lawyers, said no charges were laid against them.

President Felix Tshisekedi, who once formed an awkward power-sharing deal with Kabila, has recently accused him of sponsoring the M23 rebels who have seized east Congo's two biggest cities since January.

Kabila has also reached out to opposition politicians and civil society members to discuss the country's political future, amid criticism of Tshisekedi's response to M23's military campaign.

The military prosecutor's office had sent about 10 invitation letters to members of Kabila's People's Party for Reconstruction and Democracy, though only three appeared for questioning in the capital Kinshasa on Monday.

They were Minaku, Emmanuel Ramazani Shadary, a former interior minister and presidential candidate, and Ferdinand Kambare, national executive secretary of the party.

Minaku said earlier the officials would respond to the invitations "to avoid any suspicion" and denied links to M23 or any other armed groups.

"We are taking a purely republican approach, not one of rebellion," he told Reuters, using republican to indicate loyalty to the country.

"We clearly denounced any illicit presence of foreign forces," he said.

The latest M23 advance is the gravest escalation of a long-running conflict rooted in the spillover into Congo of Rwanda's 1994 genocide and the struggle for control of Congo's vast mineral resources.

Rwanda denies providing arms and troops to M23, and says its forces are acting in self defence against the Congolese army and militias hostile to Kigali.