ZAWIYAT ABU MUSALLEM, Egypt Kasbana Abdelaziz's house guests had barely arrived when the mob was upon them, hurling petrol bombs and smashing holes through the roof of her home.
The attackers then dragged four men - Shi'ite Muslims who had come to this Cairo suburb for a religious festival - out into the street and beat them to death.
President Mohamed Mursi condemned the "heinous crime" that happened on Sunday and promised swift justice, but his opponents accuse him and his Muslim Brotherhood of allowing ultraconservative Salafist allies to whip up anti-Shi'ite sentiment in return for their support.
"They called us infidels," Abdelaziz, said, sitting on her floor amid broken concrete, shattered glass and splintered wood. Two of her daughters stood weeping in the room behind her.
The mob killing in Zawiyat Abu Musallem has caused outrage among opposition leaders in Egypt at a time of deep political tension in the Arab world's most populous country.
Little is left of Abdelaziz's house in the Cairo suburb, an area of mud-brick and concrete-block homes, narrow dirt alleyways and fields of date palms in view of the Giza pyramids.
The kitchen is stripped bare; a battered refrigerator door lies amid dust, scraps of cloth and bricks on the floor. Daylight pours in through holes in the ceiling. An image of the shrine of Imam Ali in Iraq, one of the holiest sites in Shi'ite Islam, hangs on a wall in the ransacked bedroom.
Abdelaziz had no doubt who was behind the destruction. "It was the Salafists and the Brotherhood - they're the ones who attacked us," she said. "They did things you can't imagine."
Shi'ites are a small minority in Egypt - though still number in the hundreds of thousands - and they keep a low profile in the overwhelmingly Sunni country of 84 million. But the war in Syria, which pits mostly Sunni rebels against President Bashar al-Assad and his Shi'ite allies, has worsened sectarian hatreds across the region.
The violence in Zawiyat Abu Musallem started in the early afternoon, Abdelaziz and her daughters said, just after Hassan Shehata, a Shi'ite dignitary, arrived as a guest of her husband, a plasterer from the area.
Hundreds of men gathered in the rubbish-strewn alley outside the house when they learned Shehata was inside. "He'd only just entered and come up when we found all the people upon us," Abdelaziz said. "There was chanting - 'you Shi'ites, you infidels'. People were chanting and people were throwing bricks."
A video posted online showed a crowd dragging four men wearing robes from the house and beating them with fists and rods until they fell, bloodied and motionless, in the alley.
One comment on the video, which has gained several hundred "likes" on YouTube, addressed Shehata: "May your filthy soul lie in hell forever and ever. Amen."
Another video posted by rights activists showed dozens of men and youths looking on as several others drag the bloodied body of at least one man along a street, one pulling on what may be a rope around his neck.
In other sequences, a group of black-robed women on a crowded, narrow street chant "No God but God!" Riot police are present in the video, which shows an officer yelling out in frustration: "They're beating us!"
Abdelaziz said she did not know what had become of her husband, Farhat, but he may have been taken to hospital after the attack.
Bahaa Anwar, a leader in Egypt's Shi'ite community, was quoted by state newspaper al-Ahram as saying Mursi and the Brotherhood were using the Shi'ites as a "scapegoat" to appease their Salafist allies.
Liberal opponents of the Muslim Brotherhood also accused the movement of stirring up sectarian passions by joining in Sunni calls for jihad against Syria's Assad and his Shi'ite allies from Lebanon and Iran.
Mursi and the Brotherhood angered Salafists by trying to improve relations with Shi'ite Iran after Mursi was elected a year ago but this month the Islamist group threw its weight behind calls for "holy war" against Assad, at a conference in Cairo.
Mursi's opponents are planning mass rallies on June 30 to call for his resignation and early presidential elections - he and the Brotherhood have staged their own shows of strength, prompting Egypt's army to warn it may step in to impose order.