CAIRO, Nov 2 (Reuters) - Gunmen killed at least seven Christians who were returning from baptizing a child at a Coptic monastery in Egypt on Friday, officials said - the most serious attack on the minority in more than a year.Six of the dead were from the same family, and another 18 people, including children, were wounded, the Coptic Church's spokesman said in a statement.Islamic State claimed responsibility for the ambush in Minya province in central Egypt, the militant group's Amaq news agency said, without providing evidence of its involvement."The jihadists targeted them with light weapons and killed 13 people and injured 18," the group said in a statement released much later in the evening."This operation comes as revenge for our chaste sisters that were arrested by the apostate Egyptian regime, and we promise more attacks to all who aid it."Egyptian security forces on Wednesday night detained six women, including the daughter of former presidential candidate and senior Muslim Brotherhood leader Khairat al-Shater.The Muslim Brotherhood has denied any links to Islamic State.The attackers opened fire mid-afternoon on two buses near the Monastery of St Samuel the Confessor in Minya, 260 km (160 miles) up the River Nile from Cairo, the church spokesman said.Footage posted on social media showed bodies inside a bus with apparent gunshot wounds. Reuters was not able to verify the authenticity of the pictures.The attackers then fled, a witness at the monastery said.Local resident Hilal told Reuters he rushed to the scene after hearing about the attack and saw the militants on the road."Some of us came to try and block the road. There were three four-wheel drive vehicles and the militants opened fire ... The militants wore white thobes and checkered head-dresses," he told Reuters."DARK TERRORISM"Islamic State and affiliated groups have claimed responsibility for a series of attacks on Christians, including one that killed 28 people in almost the same spot in May 2017 https://www.reuters.com/article/us-egypt-security/he-said-he-was-christian-they-shot-him-says-son-who-saw-father-die-idUSKBN19B176.Egypt's army and police launched a crackdown on the militant groups in February, targeting the Sinai Peninsula as well as southern areas and the border with Libya.President Abdel Fattah al-Sisi said he mourned the victims as martyrs and vowed to push ahead with the campaign."I assert our determination to fight dark terrorism and to pursue the perpetrators," he said on Twitter.Saudi Arabia, Iran, the United Arab Emirates, Jordan and Kuwait all condemned the attack.The European Union said it was a "stark reminder of the security challenges that Egypt is facing."Egypt says fighting Islamist militants is a priority to restore stability after the years of turmoil that followed the "Arab Spring" protests in 2011.The public prosecutor said a team of investigators has been despatched to the scene of the attack.