MINYA, Egypt — The Islamic State group on Saturday claimed responsibility for the attack on a bus carrying Christians on their way to a remote desert monastery south of the Egyptian capital, Cairo, which killed 29. The claim of responsibility takes to four the number of deadly attacks targeting Christians since December that the extremist group says it’s behind. The Egyptian Cabinet, meanwhile, said 13 victims of Friday’s carnage remained hospitalized in Cairo and Minya province, where the attack took place. Egypt’s government has been struggling to contain an insurgency by Islamic militants led by an Islamic State affiliate that is centered in the northern region of the Sinai peninsula.