WASHINGTON - The chairman of a Senate panel Tuesday blocked $650 million in military aid for Egypt in a sign of Washington's ambivalence over support for the authoritarian military government in Cairo.

Sen. Patrick J. Leahy, a Vermont Democrat and chairman of the subcommittee responsible for foreign aid, said in a speech on the Senate floor that he could not approve the release of the aid after an Egyptian court Monday sentenced to death 683 supporters of the Muslim Brotherhood, the movement of Egypt's ousted Islamist president.

"We can't stand here and say, Golly, gee whiz, we're disturbed by hundreds of people being sentenced to death after a few minutes in a mass trial," Leahy said.

The court on Monday sentenced the Muslim Brotherhood's supreme guide, Mohamed Badie, and 682 others to death for an attack on a police station and the killing of an officer during clashes last summer.

Secretary of State John Kerry, concerned about Cairo's human-rights record but eager to support its crackdown on terrorism, last week freed the aid after holding up the money and 10 Apache helicopters for six months to build pressure for democratic reform. Though Congress can hold up the money, Kerry still plans to send Egypt the helicopters.

Leahy, who has the leverage to hold the money indefinitely, said he would not release it "until we see convincing evidence the government is committed to the rule of law."

Congress and the Obama administration have been ambivalent about the Egyptian military that overthrew President Mohammed Morsi in July. Though U.S. officials are eager for Egypt to move against the growing extremist threat in Sinai, in part to protect Israel, they are not convinced that the government will move on a more democratic path, as it has promised.

Kerry, in an appearance Tuesday at the State Department with Egyptian Foreign Minister Nabil Fahmy, said he intended to discuss with Fahmy "disturbing decisions within the judicial process."

"We really are looking for certain things to happen that will give people the sense of confidence about this road ahead," he said.

Fahmy insisted Egypt was on a path to greater democracy.