At least seven people were killed and 20 wounded on Friday when gunmen opened fire on three buses carrying Coptic Christians.
The attack took place near the remote desert monastery of St Samuel in Minya province.
President Abdel Fattah El-Sisi offered condolences for the victims and vowed to push ahead with a campaign to crush militants in the country.
“I wish a speedy recovery to the injured and assert our determination to fight dark terrorism and to pursue the perpetrators,” El-Sisi said.
Security forces rushed to the scene and ambulances ferried the injured to hospitals nearby, a security source told Arab News.
Coptic Orthodox Church spokesman Bouls Halim said the death toll in the attack was likely to rise, AP reported.
Daesh, which has carried out similar attacks, said it was behind the massacre. The extremist militants have been fighting security forces in the Sinai Peninsula and along Egypt’s border with Libya.
Friday’s attack is the second to target pilgrims heading to the St Samuel monastery in as many years. A Daesh attack on a bus convoy in Minya in May 2017 killed at least 29 people.
A spokesman for the monastery, Peter Lahami, said there were people with very serious injuries and that the death toll could increase.
Another church source said the bus had come from Margarijs in Sohag.
Coptic expert Robier Al-Faris said that after Egypt’s major security operation in Sinai to clear militants from the peninsula, some of the extremists had spread south to continue attacks.
The Egyptian security forces have recently carried out several raids on militant targets, training camps and support centers in Upper Egypt.