M23 official Museveni Sendugo said rebel forces already pulled back about 3 miles from the frontline to allow the investigation into the Thursday incident, the BBC reported Friday.
The country's army has denied accusations from Rwandan officials that it fired the shells.
Both the Democratic Republic of Congo and the United Nations have accused Rwanda of backing the M23 rebels, which Rwanda denies.
The M23 group, meanwhile, has boosted its delegation in a bid to resume stalled peace negotiations with the DRC government in Kampala, Uganda, the BBC reported.
Rene Abandi, the head of the M23 delegation, said his group's delegation is committed to finding a political solution to end the fighting.
He blamed the DRC government delegation of failing to show up for negotiations and was firing on Goma instead.
"We are committed to dialogue and peace although the Kinshasa government side is not here for the talks," Abandi said. "We remain committed to the talks and our emphasis is on signing a bilateral cease-fire with the Kinshasa [government]."
M23 previously called for a formal truce to be signed with the DRC, but government officials said they prefer the issue be addressed by military leaders under the regional Joint Verification Mechanism of the International Conference on the Great Lakes Region, the BBC said.
Peace negotiations began after the organization met in Kampala in November to discuss how to resolve the security situation in eastern DRC.
The U.N. Security Council Thursday repeated its demand to M23 and other rebel groups in the DRC to stop "all forms of violence and lay down their arms," amid the renewed fighting.
In a statement, the U.N. Security Council called on the militants to "immediately and permanently disband and lay down their arms," saying the council was prepared to adopt "additional targeted sanctions against those acting in violation of the sanctions regime and the arms embargo."