The Jundallah (Soldiers of God) group claimed responsibility for the bombings, which targeted a Shia mosque attended by members of the elite Revolutionary Guards in the predominantly Sunni city of Zahedan in the Sistan-Baluchestan province.
Geneneral Ahmad Reza Radan, Iran's deputy police chief, told the semiofficial Fars agency that police had arrested people who "intended to create insecurity in the city of Zahedan after the bombing".
Other government officials lashed out at foreign powers, blaming them for the deadly bombings.
'Act of mercenaries'
"This blind terrorist act was carried out by the mercenaries of the world arrogance (the Western powers)," state television's website quoted Ali Abdollahi, the deputy interior minister, as saying.
"The agents of this crime were trained and equipped beyond our borders and then came into Iran."
The European Union, the United Nations and the United States have all incidentally condemned the attack.
Tehran has long charged that Washington has provided support to Jundallah as part of efforts to destabilise the Islamic regime by fomenting unrest among ethnic minorities in sensitive border areas.
But on Friday Barack Obama, the US president, condemned the "outrageous terrorist attacks," while Ban Ki-moon, the UN chief, blasted a "senseless act of terrorism" and Catherine Ashton, the European Union foreign affairs head, condemned "these cowardly terrorist attacks".
Mostafa Mohammad Najjar, the Iranian interior minister, pointed the finger at Israel, charging that Iran's arch-foe was seeking to stir up sectarian tensions.
"The terrorist act by the Zionists had a number of objectives, including creating division between Shias and Sunnis," the ISNA news agency quoted Najjar as saying.