The US state department said Ms Porras had "repeatedly obstructed and undermined anti-corruption investigations in Guatemala".
Ms Porras has denied any wrongdoing and said that fighting corruption has been her priority.
On Monday, she was sworn in for a second four-year term in office.
As he re-appointed her, Guatemalan President Alejandro Giammattei described Ms Porras as "a professional who meets all the constitutional requirements" to serve another term.
He also said that the independence and autonomy of the attorney general's office would be strengthened so that it "will not be used ever again by [Guatemalan] nationals or foreigners to impose an ideological or political agenda".
The US state department had added Ms Porras and her husband to a list of "corrupt and undemocratic actors" in September.
In a tweet published on Tuesday, US Secretary of State Antony Blinken again accused her of corrupt acts.
In a statement, Secretary Blinken also said that Ms Porras had obstructed anti-corruption investigations "to protect her political allies and gain undue political favour".
Ms Porras came in for criticism in Guatemala and abroad after she sacked the head of Guatemala's anti-corruption unit, Juan Francisco Sandoval, in July.
Hundreds took to the streets in protest at his removal from office.
Mr Sandoval fled the country hours after he was sacked, but since then at least six other anti-corruption prosecutors have been arrested on Ms Porras's orders.
They are facing charges ranging from obstruction of justice to abuse of authority.
Their supporters say the charges against them are fabricated and aimed at preventing them from investigating corruption at the highest levels of government.
Ms Porras insisted during her inauguration speech that under her leadership the attorney general's office has acted "without any bias or political ideology, strictly focussing on its constitutional and legal role".