The Islamic State group on Wednesday claimed responsiblity for an attack by gunmen on a bus that killed at least 43 Shiites in Pakistan's biggest city Karachi.

"Thanks be to Allah, 43 apostates were killed and around 30 were wounded in an attack carried out by Islamic State soldiers on a bus transporting Shiite Ismaili infidels in the city of Karachi," the extremist group said in a statement posted on jihadist Twitter accounts.