A Sunni militant group, Jaish-ul Adl, has claimed responsibility for an attack that killed 14 Iranian border guards in the country's mountainous southeast, ISNA news agency reported Sunday.
The hitherto-unknown Jaish-ul Adl (Army of Justice) said on its website that it was behind Friday's attack, calling it a "severe blow" for the Iranian government.
The assault was launched in response "to the crimes of the Revolutionary Guards in Syria," the group said in a statement posted on jaishuladl.blogspot.fr.
Photographs on the website show masked gunmen holding up flags similar to those of jihadist groups in Syria and Libya, with the Arabic inscription: "There is no God but God and Mohammed is his messenger".
Opposition groups in war-ravaged Syria have charged that Tehran is sending members of its elite Revolutionary Guards to fight alongside forces loyal to President Bashar al-Assad.
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Friday's attack in the Iranian region of Sistan-Baluchestan on the Pakistani border killed 14 border guards and wounded seven others, prompting Iran to hang 16 prisoners at a jail in the province.
Tehran said the militants crossed over from Pakistan fled back across the border after the attack.
Deputy Interior Minister Ali Abdollahi called on the Pakistani government to "take measures to control the border more seriously".
The Revolutionary Guards meanwhile said the incident was "commanded and supported by the intelligence services of the dominant power," referring to the United States.
Sistan-Baluchestan province is home to a large community of minority Sunni Muslims, unlike the rest of Shiite-dominated Iran.
Another Sunni militant group Jundallah (Soldiers of God), whose leader Abdolmalek Rigi was hanged in June 2010, has also launched attacks on civilians and officials in Sistan-Baluchestan.
Drug traffickers have also clashed with members of the security forces in Sistan-Baluchestan in the past.