Six people were killed late Saturday when violence erupted between Egypt's Muslims and Coptic Christians in the poor Cairo neighbourhood of Imbaba, DPA reported.
At least two of those killed were Muslims, the Health Ministry said.
The violence, which also left more than 50 people injured, was sparked when hundreds of conservative Muslims marched to a nearby church. They believed a young woman was being held hostage inside the church after recently converting to Islam and marrying a Muslim.
According to witnesses, gunshots were fired and Molotov cocktails were thrown at the scene.
Shortly after the incident, Coptic Christians converged in front of the US Embassy in Cairo. They vowed to remain outside the embassy until the ambassador meets them to discuss what they said are injustices against minority Christians.
Romantic relations between Muslims and Coptic Christians have led to violence in the past, with both sides strictly prohibiting women from marrying a man of the other religion.
The case of two priests' wives, who are prohibited from divorce under the Coptic Church, has led to continuous protests by conservative Muslims who believe the women converted to Islam as a means of getting out of their marriages.
The women's whereabouts are unknown and protesters have accused the government of returning the women to the Coptic Church to appease church leaders.
In March, 13 people were killed in sectarian clashes around the Cairo neighbourhood of Manshiyet Nasr after a church was torched in the village of Sol, south of the capital.
Coptic Christians comprise around 10 to 15 per cent of the population in predominantly Muslim Egypt.