Nasser Shiyoukhi/AP Photo

CAIRO - The party of ousted Egyptian President Mohammed Morsi has called on its supporters to rise up against the Egyptian army after it shot and killed 42 protesters at dawn on today.

At least one soldier was also killed and more than 300 were wounded.

It was the deadliest incident since the political unrest began a week ago, deepening divisions between Morsi's Islamist supporters and the secularists who called for his ouster.

Both sides disputed who fired the first shot in front of the Republican Guard headquarters. The army said that it was fired upon by "armed terrorists," while the wounded all said the army fired bullets, birdshot and tear gas as they started to pray.

"We were starting morning prayers when we started hearing gunfire," said Mahmoud Fouad, 29, who was hit in the leg. "They started shooting at us, bullets flying past our head. People were dying in front of me and everyone was getting hit in the back."

The health ministry reported the death and wounded toll on state television. The political arm of Morsi's Muslim Brotherhood issued a statement calling "on the great Egyptian people to rise up against those who want to steal their revolution with tanks and armored vehicles, even over the dead bodies of the people."

The military ousted Morsi from power last Wednesday, saying it was heeding calls from the Egyptian people, millions of which had taken to the streets demanding Morsi step down. The move infuriated Morsi's supporters who have protested that he is the country's legitimately elected president. Morsi won the presidential election last June with 51.7 percent of the vote in the first democratic elections in the country's history.

The Brotherhood has repeatedly said its members will protest peacefully, but has warned that the military takeover will drive some to violence.

"Nothing like today has happened before," senior Muslim Brotherhood leader Mohamed Beltagy told ABC News near the Rabaa al-Adawyia mosque where the group has been protesting and where many of the dead and wounded were brought. "It's necessary and expected that Egyptians would come and stand up against military rule and ask them to step down," he said.

At a press conference today, military spokesman Ahmed Ali said the confrontation began when an armed group attacked the soldiers guarding the Republican Guard building. They used Molotov cocktails and fired live ammunition, Ali said. He also showed a video clip of a protester firing a gun at a line of soldiers. He also rejected claims that children were killed, saying the pictures circulating online are from the war raging in Syria.

"Egypt is aiming for a genuine democratic state that will dazzle the world," said Ali. "Egypt will not be built by a certain religious current. Egypt will be built by all Egyptians, regardless of religious or political orientation. No citizen will be excluded."