The United Nations human rights office says Congolese security forces targeted U.N. monitors, preventing them from doing their jobs, while using excessive force against demonstrators who were protesting against the government.

The U.N. says police forces used tear gas and reportedly fired live ammunition, killing at least six people and injuring at least 68 others on Sunday. One of those injured was a U.N. human rights officer who was kicked and punched by security forces in the capital, Kinshasa.

Thousands joined the nationwide protests organized by Catholic church activists calling for President Joseph Kabila to step down amid long-delayed elections. The vote had been set for late 2016.

U.N. spokeswoman Ravina Shamdasani says police arrested 121 people.

The U.N. urges Congo's government to investigate where excessive force was used.