The Christians were traveling to St. Samuel the Confessor, around 62 miles northwest of the city of Minya, when they came under fire, the Interior Ministry said.
It was the latest assault directed at Egypt's increasingly embattled Christian minority, following two church bombings last month that killed more than 45, also claimed by the group.
Hours after the Friday's attack, Egypt's air force launched six strikes over its western border, targeting jihadist training camps in the Libyan port city of Derna, which is controlled by jihadists close to Al-Qaeda.
Announcing the strikes in a TV speech late on Friday, the president promised to "protect our people from the evil".
The ambassador said that combating intolerance and providing protection to Egyptians of different faiths should be a top priority, adding that extremists should not be allowed to divide the Egyptian society.
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It was quite an emotional conversation. "It wouldn't be easy, but as far as it's possible, that's what they want". Filming of Aladdin is expected to commence in the United Kingdom next month.
On Sunday, Egyptian Attorney General Nabil Sadik said he referred 48 suspected Islamic State militants to a military court over the bombing of Coptic churches. The Grand Mufti of Egypt, Shawki Allam, condemned the perpetrators as traitors. The armed assailants killed at least 29 Coptic Christians.
"The terrorist incident that took place today will not pass unnoticed", Sisi said.
The videos surfaced on social media networks on Sunday, two days after 29 were killed in the attack on a desert route south of the capital.
"They chose death", said Makarios, who has been an outspoken critic of the government's handling of anti-Christian violence in Minya, where Christians account for more than 35 percent of the population, the highest anywhere in Egypt. Following the attacks in April, Egyptian President Abdul Fattah al-Sisi declared a three-month state of emergency.
The Egyptian affiliate of IS has also previously killed several Copts in North Sinai, forcing dozens of families to flee in January.
He said the attack will not pass easily. One report said that as many as 10 attackers dressed in military uniforms drove up in three trucks, stormed the bus, demanded that the passengers recite the Muslim profession of faith, and then opened fire.
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