A medical official said the American died of gunshot wounds at a hospital. The official spoke on condition of anonymity because he was not authorized to speak to the press.
The Alexandria health department reported an Egyptian also died from a gunshot wound to the head. It was not immediately known if that victim was a Morsi opponent or supporter.
The country witnessed a wave of attacks against Muslim Brotherhood offices across the country. The Brotherhood's media spokesman, Gehad el-Haddad, said on his Twitter account that eight of his group's headquarters were attacked and looted, and two were burned down.
He accused thugs, remnants of the old regime, including members of Mubarak's disbanded National Democratic Party of being behind the attacks.
Much of the violence was in the provinces of the Nile Delta, north of Cairo.
Protesters stormed an office of the Brotherhood, attacked members inside, injuring 10, and set the office on fire in the city of Shubrakheit, the state news agency said. Others stormed a Brotherhood office in the coastal city of Baltim, destroying electronic equipment, and another of the group's branches was torched in the city of Aga.
Hundreds of protesters in the city of Bassioun threw stones at Freedom and Justice Party offices, tearing down the party sign.
The Brotherhood says at least five of those killed this week were its members. Some people "think they can topple a democratically elected President by killing his support groups," el-Haddad said earlier on his Twitter account.
There were reports of violence from the Islamist side in the Delta as well.
At least six people were injured when an anti-Morsi march was attacked by the president's supporters in the city of Samanod, according to a security official. Attackers fired gunshots and threw acid at the protesters as they passed the house of a local Brotherhood leader, the official said.
In the city of Tanta, four men believed to be Morsi supporters tried to attack a mosque preacher during his sermon, in which he called on worshippers to stand with Al-Azhar's calls to avoid bloodshed.
In Qalioubia, north of Cairo, "popular committees" charged with managing traffic stopped a caravan of more than 90 Islamists heading to Cairo, according to a security official. The group, traveling in a bus and three minibuses, carried Molotov cocktails, clubs and gas cans, the official said.
One small bus escaped, but the others were turned over to police, the official said, speaking on condition of anonymity because he was not allowed to talk with the press.
In the Suez Canal city of Port Said, an explosion left one dead and several others wounded at an opposition rally, a security official said. But the official and a witness said the blast was caused by a butane canister hit by fireworks.
In the southern city of Minya, a stronghold of hardline Islamic groups, a security official said that men affiliated to the Gamaa Islamiya group, a Brotherhood ally, fired in the air while an opposition rally was marching in the street, causing panic.
Each side has insisted it is peaceful and will remain so Sunday, blaming the other for violence.
Tamarod, the activist group whose anti-Morsi petition campaign evolved into Sunday's protest, said in a statement it opposed "to any attack against anybody, whatever the disagreement with this person was," and accused the Brotherhood of sparking violence to scare people from participating Sunday.
Tamarod says it has collected nearly 20 million signatures in the country of 90 million demanding Morsi step down.