The United States called on Rwanda to end support for M23 rebels in neighboring Democratic Republic of Congo.
"We call upon Rwanda to immediately end any support for the M23 and withdraw military personnel from eastern DRC," State Department spokeswoman Jen Psaki said on Tuesday.
Psaki said the latest concerns over M23 follow credible evidence from Human Rights Watch that said the rebels were to blame for executions, rapes and forcible recruitment of men and boys while receiving support from Rwanda.
The HRW acknowledged on Tuesday erroneous testimony in the report but said it stands by its conclusions. Rwanda rejected the group's allegations, saying that the inclusion of incorrect testimony undermined the report.
M23 began taking parts of eastern Congo early last year, accusing the government of failing to honor a 2009 peace deal.
A UN report in June this year said the M23 recruited fighters in Rwanda with the aid of sympathetic Rwandan army officers, while elements of the Congolese army have cooperated with the Rwandan Hutu rebel group FDLR.
The report prompted the United States and European states to suspend military assistance to Kigali.
It is the first response by Washington to recent M23 clashes with Congolese government forces near Goma, the largest city in the DRC's mineral-rich eastern region.
But Washington stayed clear of directly implicating Rwandan President Paul Kagame, a US ally whose poverty-fighting programs are often heralded by donors.
The UN investigation provided the strongest evidence yet that officials from Kagame's government were providing military and logistical support to armed groups in Congo.
A 17,000-strong UN force, known as MONUSCO, and Congo troops have struggled in the past decade to stem a conflict involving dozens of armed groups and complicated by national and ethnic rivalries. A 3,000-member UN Intervention Brigade was recently deployed to fight and disarm rebels in the east.