An international rights group says Congolese security forces have killed at least 24 people since President Joseph Kabila was announced the winner of an election that international observers have deemed seriously flawed.

Human Rights Watch Thursday said the victims include opposition activists as well as people simply gathered on the street or in their homes. The report said security forces have been firing on small crowds in an apparent attempt to prevent protests.

Human Rights Watch's Anneke Van Woudenberg says these “bloody tactics” further undermine the election. She says they give the impression that the government will do “whatever it takes” to retain power.

President Kabila was inaugurated Tuesday, pledging to unify his country. But opposition leader Etienne Tshisekedi has rejected the results as fraudulent and has declared himself president, saying he will take office Friday.

The U.S. said Tuesday it is “deeply disappointed” by Congo's decision to uphold the election results without fully evaluating widespread reports of irregularities.

A statement by Secretary of State Hillary Clinton said the election was seriously flawed and lacked transparency.

Mr. Kabila has suggested that Mr. Tshisekedi use the appeals system to challenge the results.

The presidential and legislative polls were only the second free elections in Congo since it was torn apart by several years of warfare that ended in 2003.

Mr. Kabila first became president after his father's assassination in 2001, and later won office following a U.N.-sponsored vote in 2006.