A suicide bomb attack in southeastern Iran that on February 13 killed at least 27 Revolutionary Guards prompted the country’s foreign minister to ask whether the terrorism might be linked to the start of a US-led conference on the Middle East taking place in Warsaw, Poland.

Mohammad Javad Zarif, who has previously lambasted the gathering as a transparent attempt to demonise the Islamic Republic at Washington’s behest, wrote on Twitter: "Is it no coincidence that Iran is hit by terror on the very day that #WarsawCircus begins?"

He added: “Especially when cohorts of same terrorists cheer it from Warsaw streets & support it with twitter bots? US seems to always make the same wrong choices, but expect different results.”

Iranian state media said the bomber targeted a bus transporting personnel on the Khash-Zahedan road in Sistan-Baluchestan province, near the border with Pakistan.

Another 20 soldiers of the Islamic Revolutionary Guard Corps (IRGC) were wounded in the attack, the official IRNA news agency cited an "informed source" as saying.

The Sunni Muslim militant group, Jaish al-Adl (Army of Justice), which is linked to al-Qaida, has claimed that it was behind the bombing.

Jaish al-Adl has since 2012 waged an armed campaign for what it says are the rights of Iranian Sunnis, who complain Iran’s Shia establishment discriminates against them.

The group has carried out several recent attacks against security personnel in Sistan-Baluchestan. The region has a mainly Sunni ethnic Baluchi community.

The IRGC blamed "takfiri terrorists and mercenaries of the intelligence services of hegemonic powers" for the suicide attack. "Takfiri" is a term used to describe Sunni extremists who regard other Muslims as non-believers.

Jaish al-Adl also said it carried out two bombings that wounded three police officers in Zahedan at the end of January. Last October, the group kidnapped at least 10 security personnel, including several IRGC soldiers, at a border post in Mirjaveh.

Last September, gunmen killed at least 24 people at a military parade in the southwestern city of Ahvaz.

Both Islamic State and Iranian ethnic Arab separatists claimed they were responsible for that attack, but neither presented conclusive evidence.