Iran's foreign ministry summoned on Sunday the Pakistani ambassador after Tehran accused Islamabad of backing a group blamed for a suicide attack on its security forces."The Islamic Republic of Iran expects Pakistan's government and army to seriously confront ... the terrorist groups active on its border with Iran," the foreign ministry said in a statement.An Iranian official at the ministry called on Pakistan to quickly take the necessary steps for the identification and arrest of the attack's perpetrators.The suicide bombing on Wednesday killed 27 members of Iran's Revolutionary Guards travelling on a bus in the volatile province of Sistan-Baluchistan, which straddles the border with Pakistan.The attack was claimed by militant outfit Jaish al-Adl.It was formed in 2012 as a successor to the Sunni extremist group Jundallah, which waged a deadly insurgency for a decade before it was severely weakened by the capture and execution of its leader Abdolmalek Rigi in 2010.Iran Revolutionary Guards commander Major General Mohammad Ali Jafari on accused “Pakistan’s security forces” of supporting the perpetrators of the suicide bombing.Iran's supreme leader Ayatollah Ali Khamenei has also linked the perpetrators of Wednesday's attack to "the spying agencies of some regional and trans-regional countries".