(Adds State Department comments, context)
By Will Dunham
WASHINGTON, March 25 (Reuters) - The United States escalated its criticism of Egypt on Tuesday over mass trials targeting the Muslim Brotherhood, and said it would be "unconscionable" for Egypt's government to carry out the death sentences given to 529 members of the outlawed Islamist group.
U.S. State Department spokeswoman Marie Harf said the way Egypt proceeds regarding the trials and death sentences will have consequences for future American aid.
Secretary of State John Kerry said on March 12 he would decide "in the days ahead" whether to resume American aid to Egypt after suspending the funds last year over the ouster of President Mohamed Mursi of the Muslim Brotherhood and a crackdown against protesters.
The death sentences handed down on Monday by an Egyptian court and the start on Tuesday of another mass trial of the leader of the Muslim Brotherhood and 682 others "represent a flagrant disregard for basic standards of justice," Harf said.
"The imposition of the death penalty for 529 defendants after a two-day summary proceeding cannot be reconciled with Egypt's obligations under international human rights law, and its implementation of these sentences ... would be unconscionable," Harf told a new briefing.
Egypt has been among the largest recipients of U.S. military and economic aid for decades following its 1979 peace treaty with U.S. ally Israel, which agreed as a result of the pact to withdraw from the Sinai Peninsula it had seized from Egypt in 1967.
"We are determining if this assistance will stay suspended, if more will be suspended, if some will be brought back on line. And suffice to say, things like (these) outrageous, shocking, unconscionable actions that the Egyptian government is taking will, of course, have an impact on that decision," Harf said.
The United States has declined to declare Mursi's overthrow in July "a coup," but has expressed concerns over the iron-fisted crackdown on Islamists and liberals by the military-backed government in which hundreds have been killed and thousands jailed.
"We are making clear to the Egyptian government that these verdicts cannot be allowed to stand," Harf said. "The government of Egypt should be taking action to increase the freedoms of the Egyptian people, not to suppress them, thereby feeding into the exact extremism that undermines peace and security."
Harf said U.S. officials "certainly hope" Egypt changes course on carrying out the death sentences, but added that "I don't have any predictions to make about what consequences might come from this." Harf denied that the United States is "meddling" in Egypt's internal affairs by criticizing the trials and death sentences.
It remains important for the United States to maintain a relationship with Egypt "for a variety of security, economic, regional reasons," Harf added.
"It's a balance. It's a fine line. We feel we're walking that line," Harf added. (Additional reporting by Will Dunham and David Brunnstrom; Editing by Sandra Maler, Bernard Orr)