In a stern warning to Egypt's leaders, Secretary of State John Kerry said the escalating violence throughout the country Wednesday had dealt a "serious blow" to political reconciliation efforts between the military-backed interim government and supporters of ousted President Mohammed Morsi.

During a surprise appearance at the State Department, Kerry condemned the violence that killed at least 149 people nationwide, as well as the restoration of emergency rule. And he urged Egypt's interim leaders to take a step back and calm the situation.

"This is a pivotal moment for all Egyptians," Kerry said. "The path toward violence leads only to greater instability, economic disaster and suffering."

Kerry spoke earlier Wednesday with Egyptian Foreign Minister Nabil Fahmy, as well as top officials in the Middle East. President Barack Obama, on a weeklong vacation in Massachusetts, was briefed on the deteriorating situation by National Security Adviser Susan Rice.

Wednesday's assault came after days of warnings by the interim administration that replaced Morsi after he was ousted in a July 3 coup. The two sit-in camps at two major intersections on opposite sides of the Egyptian capital began in late June to show support for Morsi. Protesters _ many from Morsi's Muslim Brotherhood _ have demanded his reinstatement.