Human Rights Watch is urging U.S. President Barack Obama to use his upcoming visit to Cambodia to call for an end to human rights abuses, including alleged extrajudicial killings in the Southeast Asian nation.

The New York-based rights group said in a report Tuesday over 300 people have been killed in politically motivated attacks in Cambodia in the past two decades of Prime Minister Hun Sen's rule. The group says rather than investigate the killings, Cambodia's government has instead ignored them and in some cases even promoted those believed to be responsible.

Human Rights Watch says President Obama, who next week will become the first ever U.S. head-of-state to visit Cambodia, is in a unique position to publicly demand human rights improvements in the Southeast Asian country.

The report praised the U.S. for being “one of the most outspoken critics of the Cambodian government's human rights record.” But it said Washington's actions were not always consistent with its words, noting that U.S. officials have met with and given awards to Cambodian officials implicated in serious abuses.

During his 27 years in power, Prime Minister Hun Sen has repeatedly promised democratic and other reforms, such as creating an independent judicial system and more accountable police force. But Human Rights Watch says he has not followed through on those promises, and that foreign governments have failed to hold him accountable.

Human Rights Watch Asia director Brad Adams says it is time for governments and donors to “stop talking in generalities about rights and start confronting senior government and ruling party officials about the failure of justice” in Cambodia.