U.S. President Barack Obama has stressed to Rwandan President Paul Kagame the importance of "permanently ending all support" to rebels in the neighboring Democratic Republic of Congo.
A panel of United Nations specialists has accused Rwanda and Uganda of supporting the M23 rebel group, which recently withdrew from Goma after seizing the eastern Congolese town. Both Rwanda and Uganda have denied the charges.
The White House says Obama urged Kagame during a phone call Tuesday to fulfill pledges made in regional peace talks to find a political agreement that includes ending "impunity for M23 commanders" who have committed human rights abuses.
He says the crisis should end with an agreement that upholds the DRC's sovereignty and addresses regional security, as well as economic and governance issues.
Meanwhile, the U.S. Treasury Department issued new sanctions Tuesday against two senior M23 leaders for using child soldiers and other activities contributing to the fighting in the DRC.
It says Baudoin Ngaruye and Innocent Kaina are responsible for "terrible acts of violence," and that Kaina committed acts targeting children through killing, maiming and sexual violence.
Also Tuesday, U.N. investigators said preliminary findings of a probe into alleged violations last month in Minova, near Goma, showed 126 documented cases of rape and two killings.
A U.N. spokesman said a separate investigation by the Congolese military has resulted in the arrest of nine soldiers, including two in connection with the rapes and seven others connected to looting.
A full U.N. report on the alleged violations is to come out in January.
U.N. peacekeepers have increased their patrols in the eastern part of the DRC in recent days after receiving reports of M23 fighters around Goma. The U.N. Security Council adopted a resolution in late November demanding the rebels leave the city and stop any further advances.
U.N. spokesman Kieran Dwyer said Monday that many of the reports could not be confirmed, but that the U.N. mission in the DRC was able to confirm the presence of M23 fighters in other areas of North Kivu province. He said the situation in the region remains "tense and fragile."
M23 is made up of former rebels who were integrated into the Congolese army in a 2009 peace agreement. The rebels deserted the army earlier this year, complaining of discrimination and poor treatment.
The fighting has displaced more than 100,000 people in Congo's North Kivu province, aggravating an already serious humanitarian situation in the region.