Egypt's health ministry said there were between eight and 10 attackers dressed in military uniforms, according to witnesses.
The report quotes local health officials as saying that the attack happened on Friday while the bus was traveling on the road to the St. Samuel Monastery in the Minya governorate, about 220 kilometres, or about 140 miles, south of the Egyptian capital.
The governorate is home to a sizeable Christian minority.
"ONE THIRD OF THIS PROVINCE IS COPTIC," WHERE EGYPT ATTACK TOOK PLACE
No group immediately claimed responsibility for the attack, which came on the eve of the holy Muslim month of Ramadan. Egypt has been fighting Islamic State group-linked militants who have waged an insurgency, mainly focused in the volatile north of the Sinai Peninsula but there have been also attacks on the mainland.
Egypt has seen a wave of attacks on its Christians, including twin suicide bombings in April and another attack in December on a Cairo church that left over 75 people dead and scores wounded. The Islamic State group in Egypt claimed responsibility for them and vowed more attacks.
“It’s not the first time that such attacks have happened in Minya,” FRANCE 24’s correspondent in Cairo, Alexandre Bucciante reported. However repercussions from authorities are rare, Bucciante said.
“In fact the authorities are afraid to upset the Salafists that are very strong in this province,” he added. “At the same time one third of this province is Coptic, which makes a sort of explosive cocktail.”
Late last month Pope Francis visited Egypt in part to show his support for the Christians of this Muslim majority Arab nation who have been increasingly targeted by Islamic militants.
During the trip, Francis paid tribute to the victims of the December bombing at Cairo's St. Peter's church, which is located in close proximity to the St. Mark's cathedral, the seat of the Coptic Orthodox Church.
Following the Pope's visit, the Islamic State affiliate in Egypt vowed to escalate attacks against Christians, urging Muslims to steer clear of Christian gatherings and western embassies as they are targets of their group's militants.
Egypt's Copts, the Middle East's largest Christian community, have repeatedly complained of suffering discrimination, as well as outright attacks, at hands of the country's majority Muslim population.
Over the past decades, they have been the immediate targets of Islamic extremists. They rallied behind general-turned-president, Abdel-Fattah el-Sissi, in 2013 when he ousted his Islamist predecessor Mohammed Morsi, who hails from the Muslim Brotherhood group. Attacks on Christian homes, businesses and churches subsequently surged, especially in the country's south.
(FRANCE 24 with AP, REUTERS)