BEIRUT, Lebanon — With the Syrian conflict spilling into the Lebanese border area on Monday, United Nations investigators said civilians were bearing the brunt of indiscriminate air and ground assaults in the fighting over the future of President Bashar al-Assad.

The report was presented to the United Nations Human Rights Council in Geneva by Paulo Pinheiro, the Brazilian investigator leading a commission of inquiry. Mr. Pinheiro said that there had been a sharp escalation in indiscriminate attacks by government forces against civilians, and that the commission had collected “a formidable and extraordinary body of evidence” against those responsible.

The report, completed last month, said that both anti- and pro-government forces had committed war crimes and crimes against humanity. Mr. Pinheiro said that the evidence, including names of people and units, could support action by national or international courts.

A report released on Monday by Human Rights Watch, based in New York, raised further concerns about rights abuses by antigovernment fighters. The group documented 12 cases of extrajudicial or summary executions by groups linked to the opposition, including four killings in the town of Haffa by members of the Ansar Mohammed battalion.