In 2016, at least 25 people were killed in a suicide attack on a Christian church.
Friday's attack is the second to target pilgrims heading to the Saint Samuel the Confessor monastery in Minya province in as many years.
In the past the group has called Christians "their favourite prey".
Outside Egypt, Canadian Prime Minister Justin Trudeau and the archbishop of Britain's Coptic Orthodox Church were among those condemning the attack and expressing condolences to Egyptians.
Policemen stand beside the microbus which carried Coptic Christians when gunmen opened fire in Menyia, Egypt, Nov. 2, 2018.
Later on Friday, an IS-linked website reported that militants in Egypt with links to the group had claimed responsibility for the attack.
Sisi said Friday's attack was created to harm the "nation's solid fabric" and pledged to continue fighting terrorism. The previous attack in May 2017 left almost 30 people dead. They have also underlined the vulnerability of minority Christians in a country where many Muslims have since the 1970s grown religiously conservative.More news: Daniel Ricciardo doesn't see the point in racing 'cursed' 2018 F1 auto
The remains of a vehicle reportedly used by gunmen in the November 2 attack on a bus carrying Coptic Christians.
Angry Coptic Christians in mourning kept a vigil outside a hospital in central Egypt overnight to receive the bodies of relatives killed in a gun attack on a bus transporting pilgrims.
For its part, security forces quickly surrounded the area.
The Sohag bus had 28 pilgrims, of whom 9 were wounded, including two in a serious condition.
The Interior Ministry said police were pursuing the attackers, who fled the scene.
Attacks against Coptic Christians, who account for 10% of the nation's population, have been on the rise since 2017.
The province of Minya has become known for anti-Christian violence and questions are being asked of Egyptian authorities as to why the route taken by the bus had not been secured.