KINSHASA (Reuters) - At least 21 people were killed, 40 wounded and dozens of houses burned in weekend attacks aimed at Hutus in eastern Democratic Republic of Congo, the United Nations said on Monday, expressing alarm at rising ethnic violence.

The attacks were the latest in a series of deadly skirmishes between Hutus and other local groups. These have intensified since last month when the FDLR, a Rwandan Hutu militia operating in eastern Congo, was accused by authorities of killing at least 14 ethnic Nande in North Kivu province.

U.N. spokesman Amouzoun Codjo Martin said the weekend attacks were carried out by members of two militias, the Nande-dominated UPDI and the NDC, which is mostly made up of Nyanga, another local ethnic group.

The fighting had reached an “alarming level”, the U.N. said in a statement, and could cause “large-scale violence” in the region, as well as displacement of civilians. The U.N. has also received reports of looting, abduction and rape over the past few days.

Ethnic rivalries, foreign invasions and competition for mineral-rich land have stoked persistent conflict among eastern Congo’s dozens of rebel groups over the last two decades, costing millions of lives.

Tensions have spiked between the Hutu and neighboring communities since Congo’s army launched a military offensive last year against the FDLR, displacing large numbers of fighters and Hutu civilians.

Congolese troops and U.N. peacekeepers were forced to fire into the air last Wednesday in a nearby town to disperse Hutu and Nande villagers after the two groups clashed with machetes and batons.