Clashes on Friday in the Egyptian province of Mersa Matrouh between Coptic Christians and Muslims have left 31 people wounded, reports said.
Around 400 people were involved in the fighting, which lasted for 10 hours and left fires blazing in three homes and two cars, one security official told AFP.
27 people, both Christians and Muslims were arrested.
According to one Coptic bishop, the fighting erupted after Muslim extremists attacked a Coptic center and nearby homes following a sermon by a radical sheik.
Officials said that rioters were upset about a new fence being built around the center.
The fighting occurred the same day as the US Commission on International Religious Freedom (USCIRF) released a statement denouncing lax prosecution of Egyptian Muslims accused of committing violent acts against Coptic Christians.
The statement focused on the February 22 acquittal of four Muslim men who were accused with the 2009 murder of Farouk Attallah.
According to reports, Mr. Attallah's Christian son was involved in a romantic relationship with a Muslim girl. The Muslim men allegedly had planned to attack the young man, but when the attackers could not find him, they killed his father. The court stated the reason for the acquittal was insufficient evidence.
"This is one of more than a dozen incidents USCIRF has followed in the last year or so in which Coptic Christians have been the targets of violence," said USCIRF chair Leonard Leo, who led a USCIRF fact-finding delegation to Egypt in January. "This upsurge in violence and the failure to prosecute those responsible fosters a growing climate of impunity."
"We call on the government to appeal the verdict in the Attallah murder and bring the perpetrators to justice," he added.
The USCIRF also noted the January 6 shootings of six Coptic Christians, which three Muslim men are currently on trial for, and called on the Egyptian government to "prosecute the perpetrators to the fullest extent of the law through a fair and transparent trial."
The incident, which occurred during a Christmas eve celebration in Naga Hammadi, is considered one of the worst acts of sectarian violence in the region in decades and received widespread condemnation from the international community.
The Rev. Michael Kinnamon, general secretary for the National Council of Churches (NCC), condemned the attacks as a flagrant denial of the love of God as testified to in the New Testament, the Hebrew Scriptures and the Qur'an.
"Violence in God's name is not only an obvious corruption of Scripture, it demonstrates an appalling disregard for the loving and just God who commands us to live together in peace," Kinnamon said. "What is especially painful is that this recent violence took place during a celebration of the birth of the one who Christians call the Prince of Peace and who Muslims call a holy prophet."
A verdict on the three Muslim men, who have all pleaded not guilty, is scheduled to be given on March 20.
Coptic Christians make up about 10 percent of Egypt's 80 million population, the rest of which are mostly Sunni Muslims, and are often subject to discrimination and harassment.
Coptic churches can only be built with special presidential permission while mosques can be constructed freely.
Egypt has been on the USCIRF "Watch List" since 2002 as a country with serious religious freedom violations, including widespread problems of discrimination, intolerance, and other human rights violations against members of religious minorities, as well as disfavored Muslims.