Egypt's Coptic Orthodox Church says gunmen have opened fire on a bus carrying Christian pilgrims traveling to a remote desert monastery, killing at least seven.
A number of people were also injured in the attack in the Minya region, south of the capital Cairo.
A security official confirmed the attack in the central province of Minya, adding that there were "dead and wounded".
No group claimed responsibility for the attack.
The Interior Ministry, which oversees the police, and the security officials said Friday's attackers used secondary dirt roads to reach the buses carrying the pilgrims, who were near the monastery at the time of the attack.
"I am mourning with deep sadness the martyrs who fell today at the hands of traitors who are trying to harm the tightly-knit fabric of the nation", Sisi said.
Hulk Hogan Kicks Off WWE Crown Jewel As Host (Pics, Video)
Joe has taken The Leader of the Cenation's place and will reignite his rivalry with The Phenomenal One today. Shane McMahon won the WWE World Cup after introducing himself as a late replacement for the injured Miz.
"I assert our determination to fight dark terrorism and to pursue the perpetrators", he said on Twitter.
Those attacks, all claimed by the Islamic State group, left at least a 100 people dead and led to tighter security around Christian places of worship and other Church-linked facilities.
Church spokesman Bouls Halim said the death toll in Friday's attack was expected to rise.
The military offensive - Dubbed "Sinai 2018" - has killed more than 450 jihadists, while about 30 Egyptian soldiers have been killed during this year's operation.
Just last month, an Egyptian military court handed down death sentences to 17 people convicted in a series of fatal attacks on Christians throughout the country since December 2016.
Copts have long complained of discrimination in Egypt and IS is not the only group to have launched sectarian attacks against the community.
In a somber message of his own, Tawadros said in a video clip released by the church that the latest attack would only make the Christians stronger.