Attacks on Egypt's Coptic Christian minority by supporters of ousted president Mohammed Morsi have intensified since the bloody crackdown of Wednesday, with violence reported against churches, monasteries, schools, Christian-owned shops and individuals.
The Egyptian Initiative for Personal Rights said that 25 churches had been targeted and burned over two days across the country in towns hundreds of miles away from Cairo.
The Bible Society in Fayoum, the YMCA, the Evangelical Foundation & Oum al-Nour, and other Christian organisations such as the House of Father Angelos and Dahebeya Nile Boat in Menya were targeted.
In Luxor, Coptic-owned shops along with a pharmacy and hotels were attacked.
Coptic Christians account for an estimated 10 per cent of the country's 85 million population. The Egyptian military pledged to rebuild the burned churches, state media reported.
Muslim Brotherhood members and supporters were angered by Coptic Pope Tawadros' decision to bless the 3 July military coup.
President Obama said: "We call on those who are protesting to do so peacefully and condemn the attacks that we've seen by protesters, including on churches."
A mob set fire and destroyed one Seventh-Day Adventist church in Assiut, 200 miles from Cairo.
According to experts, top Islamist preachers overseas, including Sheikh Yusif al-Qaradawi, encourage violence against the Copts for their support of the military coup. In a video, he said that Christians "were recruited [by Egypt's military] to kill innocent Muslims".
Bishop Anba Suriel of the Coptic Orthodox Church in Melbourne, Australia, said on Twitter that the attacks on Copts "are unprecedented in the modern era".
The latest backlash started when pro-Morsi supporters attacked churches in Dilga, Menya and Sohag. The 4th-century Virgin Mary Monastery of Minya was burned to the ground.
Earlier in August, al-Qaida leader Ayman al-Zawahiri said that Tawadros wanted to establish a Coptic state in Egypt.
In July, suspected Islamist militants killed a Christian merchant in the northern Sinai peninsula in the first post-Morsi backlash.
Sectarian violence against Coptic Christians has increased in recent years. In January 2011 a car bomb exploded outside Alexandria Coptic Orthodox Church, killing 21 and injuring at least 79.
In the worst post-revolution incident, 28 people, mostly Copts, were killed during a sit-in in front of the Maspero television building in Cairo, where they had gathered to protest against the demolition of a church in upper Egypt.