American president Barack Obama’s Egypt policy is severely tested as the Arab nation’s military forcefully disbands tens of thousands of Muslim Brotherhood supporters who were protesting last month’s removal of President Mohamed Morsi from office.

As is usual during a time of confrontation, the exact death toll is unknown. The Egyptian Health Ministry originally counted 278 people dead as a result of the police dispersal of the mass demonstrations but reports now speculate up to five hundred casualties, most them civilians but also policemen.

What is certain is that the military’s decision to move into the protest camps in full force — tear gas, live ammunition, bulldozers and helicopters were used — will make reconciliation between Egypt’s Islamist and secular factions all the more difficult.

Defense chief Abdul Fatah Sisi, with the full support of the interim president and prime minister, had threatened to remove those demanding Morsi’s reinstatement from the streets since last week. Tens of thousands, including women and children, were present in the camps — a reason for the military to postpone its decision. But when American, Arab and European mediation failed to bridge the gap between Morsi’s supporters and the interim government, it appears the security forces became convinced that further delay would have only encourage more Egyptians to take to the streets.

According to reporters on the scene, police moved into the main protests in the early morning on Wednesday. Bulldozers employed by the police tore down makeshift brick walls that were erected by the protesters weeks earlier before tear gas was shot into the crowds to break them up. Demonstrators threw rocks and Molotov cocktails at the troops, prompting them to open fire.

Dozens upon dozens of demonstrators were mowed down and hundreds more injured and sped to hospitals across the capital. Blood soaked the pavements. Hundreds of people were arrested and a state of emergency declared later in the day. Vice President Mohamed ElBaradei, the former International Atomic Energy Agency chief, resigned in protest.

The United States, the Egyptian army’s most powerful backer, is predictably upset by what occurred. Secretary of State John Kerry called the army’s violence wholly unfounded. The White House condemned the army’s actions in similar terms with President Barack Obama holding a special news conference during his summer vacation to announce that an annual American-Egyptian military exercise would be suspended. The European Union’s foreign policy chief, Baroness Catherine Ashton, urged (PDF) Egypt’s military to practice the “utmost restraint.”

The United States has repeatedly stressed that it was not taking sides in Egypt’s political crisis since it urged former strongman President Hosni Mubarak to step down in early 2011. The violence in Cairo might persuade it to revise that policy. The cancelation of a joint military drill could be a step in this direction but it will not be enough to signal the country’s disgust with what Egypt’s generals ordered this week.

Congress could play a role. It authorizes the hundreds of millions of dollars in military aid the Egyptian armed forces receive from the United States every year. Senators from both parties were already calling on the administration to suspend the aid after last month’s coup. Such calls will grow louder.

President Obama hasn’t yet followed through on those calls for fear of losing influence in the Arab world’s most populous nation. If the bloodshed worsens, however, and more Muslim Brotherhood activists are arrested without charge, if not killed, he might have little choice but to acquiesce. Without at least a suspension in aid, Egypt’s military leaders have little reason to stop what they’re doing.