Members of Iran's Revolutionary Guards
Members of Iran's Revolutionary GuardsReuters

At least 27 people were killed in a suicide attack on Wednesday on a Revolutionary Guards bus in southeastern Iran, AFP reports.

"The suicide attack on an Islamic Revolutionary Guards Corps personnel bus happened on the Khash-Zahedan road," said the IRNA news agency.

A picture released by the semiofficial Fars news agency showed a hulk of twisted metal lying by the side of a road, unrecognizable as a bus.

The Guards issued a statement confirming the attack. It said the troops were returning from the border.

"In this terrorist attack 27 of Islam's brave warriors were killed and 13 were wounded," the statement read, according to AFP, accusing "world domination and Zionist intelligence agencies" of supporting the attackers.

The attack took place in the volatile southeastern province of Sistan-Baluchistan which has a large, mainly Sunni Muslim ethnic Baluchi community straddling the border with Pakistan.

The SITE Intelligence Group reported that the attack was claimed by Jaish al-Adl, a group formed in 2012 as a successor to the Sunni extremist group Jundallah (Soldiers of God), which waged a deadly insurgency against Iranian targets over the past decade.

Sistan-Baluchistan has been the scene of other attacks in the past.

On January 29, three members of an Iranian bomb squad sent to the scene of an explosion in its capital Zahedan were wounded when a second device blew up as they were trying to defuse it, police said at the time.

In early December last year, two people were killed and around 40 others wounded in the port city of Chabahar, also in Sistan-Baluchistan, in an attack which Zarif at the time blamed on "foreign-backed terrorists" -- a reference to Sunni Muslim extremists.

The bloodiest attack in recent times to have hit Iran took place in September when terrorists killed 24 people at a military parade in the southwestern city of Ahvaz.

The attack was claimed by the Islamic State (ISIS), but it was also claimed by a movement called the "Ahwaz National Resistance", an Arab separatist group.

ISIS had posted a video of three men who allegedly carried out the attack and later threatened to carry out new attacks in Iran, saying the Islamic Republic is "flimsier than a spider's web, and with God's help, what comes will be worse and more bitter".

Iranian President Hassan Rouhani has accused the US and the Gulf states of responsibility for the Ahvaz attack.

Similarly, Iranian Foreign Minister Mohammad Javad Zarif blamed the attack on “regional terror sponsors and their US masters”.

US Secretary of State Mike Pompeo was subsequently asked about Zarif’s comments in an interview and replied, “When you have a security incident at home, blaming others is an enormous mistake. And the loss of innocent life is tragic, and I wish Zarif would focus on keeping his own people secure rather than causing insecurity all around the world.”