The United States voiced disappointment Thursday over Guatemala's quick naming of a controversial new anti-corruption investigator, whose predecessor's dismissal drew protests from Washington.

The "sudden appointment" on Tuesday of Rafael Curruchiche as head of the anti-corruption unit "does not add confidence in the body's ability to independently investigate and prosecute corruption cases," State Department spokesman Ned Price told reporters.

"Our position remains that it is essential that FECI is able to function and its prosecutors and its analysts are empowered to continue to investigate cases to maintain the fight against corruption in Guatemala," he said, using the unit's Spanish acronym.

A demonstrator demands the resignation of Guatemala's President Alejandro Giammattei and Attorney General Maria Consuelo Porras after the dismissal of the special prosecutor for corruption in July 2021
A demonstrator demands the resignation of Guatemala's President Alejandro Giammattei and Attorney General Maria Consuelo Porras after the dismissal of the special prosecutor for corruption in July 2021 AFP / Johan ORDONEZ

Opposition MPs have accused Curruchiche of corruption, with media reports alleging that, in his job investigating electoral crimes, he offered protection to businesspeople suspected of illegal political financing.

Attorney General Consuelo Porras went ahead with the appointment, even though President Joe Biden's administration last month said it lost confidence in her and would suspend cooperation after she abruptly fired previous anti-corruption chief Juan Francisco Sandoval.

Sandoval, who had been presented an award earlier in the year by US Secretary of State Antony Blinken for his anti-graft work, fled Guatemala after his dismissal as he voiced fears for his safety.

The Biden administration has identified the fight of corruption -- as well as addressing poverty, violence and climate change -- as a key element in a strategy to stop the mass migration of Central Americans, which has become a major political issue in the United States.