U.S. Senator Patrick Leahy, chairman of the Senate subcommittee that oversees foreign aid, said on Tuesday he would not approve sending funds to the Egyptian military, according to Reuters.
Leahy denounced what he termed a "sham trial" in which a court sentenced 683 supporters of former Islamist President Mohammed Morsi to death.
The decision by Leahy could further complicate the Obama administration's difficult relationship with Egypt, one of Washington's most important strategic allies in the Middle East.
The Pentagon said last week it would deliver 10 Apache attack helicopters and $650 million to Egypt's military.
Leahy said, however, "I'm not prepared to sign off on the delivery of additional aid for the Egyptian military. I'm not prepared to do that until we see convincing evidence the government is committed to the rule of law."
The 683 members of the Muslim Brotherhood who were convicted on Monday, were accused of charges related to violent riots in the central Egyptian city of Minya in August, including the murder of a police officer.
Among those convicted was the Islamist group's Supreme Guide Mohammed Badie, who was arrested in late August after being discovered hiding in a building in Cairo’s Nasr City district.
Leahy said, according to Reuters, that he would be watching the situation in Egypt with "growing dismay" even if he were not chairman of the State and Foreign Operations Subcommittee, denouncing "a sham trial lasting barely an hour."
"It's an appalling abuse of the justice system, which is fundamental to any democracy. Nobody, nobody, can justify this. It does not show democracy. It shows a dictatorship run amok. It is a total violation of human rights," the Vermont Democrat said.
In October, the United States announced it would cut hundreds of millions of dollars in aid to Egypt over its displeasure with the military's pace of restoring democracy following Morsi’s ouster.
U.S. law forbids sending aid to countries where a democratic government was deposed by a military coup, though Washington has never qualified Morsi’s ouster as a "coup" and has been cautious about doing so, choosing only to condemn the violence in the country.
Administration officials did not comment specifically on Leahy's remarks, but said they would discuss the issue with members of Congress.
Secretary of State John Kerry had an hour-long meeting on Tuesday with Egyptian Foreign Minister Nabil Fahmy in Washington and made clear the United States was "deeply disturbed" by recent events in Egypt, State Department spokeswoman Jen Psaki was quoted by Reuters as having said.
"These actions represent a setback and make it more challenging to move forward," she said at a briefing. Psaki said the State Department will be briefing members of Congress and hearing their concerns.