The United States has said it is alarmed by an escalation in fighting in eastern Democratic Republic of Congo between M23 rebels and Congolese soldiers, and has again called on neighbouring Rwanda to stop supporting the rebels.
After a two-month lull, fighting between the army and the M23 has erupted sporadically since mid-July in North Kivu, a chronically unstable region with the mining hub of Goma as its capital.
The State Department condemned attacks by the M23 that killed at least three people in Goma on Saturday. It also expressed concern over reports by the United Nations of shelling by the M23 into Rwanda territory.
"We urgently call on (the) DRC and Rwandan governments to exercise restraint to prevent military escalation of the conflict or any action that puts civilians at risk," State Department spokeswoman Marie Harf said in a statement.
"We are deeply concerned about evidence of increasing ethnic tensions in Goma and call on all parties to avoid any actions that could exacerbate such tensions."
A 3,000-member UN Intervention Brigade has been deployed to fight and disarm rebels in the east and has this week been drawn into the fighting for the first time, firing artillery and fighting alongside the Congolese army on the front lines.
The spokeswoman praised UN efforts to protect civilians, after the world body announced it had opened a probe into accusations by residents that peacekeepers killed two people who tried to storm its Goma base during a protest.
Harf said the US was ready to consider further targeted sanctions against M23 rebel leaders and other armed groups. Some M23 leaders are already subject to UN Security Council sanctions.
Washington urged the UN mission in Congo, MONUSCO, to investigate charges of cross-border shelling. Rwanda said five mortar bombs had fallen on Rwandan villages on Friday, following a rocket the previous day, and blamed Congo's army.
Rwanda twice invaded its larger neighbour in the 1990s and sponsored rebels trying to topple the Kinshasa government.
Millions have died since then in Congo's eastern border area, a patchwork of rebel and militia fiefdoms in an area rich in tin as well as tungsten and coltan ores.
A UN report in June 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, which Rwanda denies.