A suicide bombing attack outside a mosque in Iran's southeastern Sistan-Baluchistan province that killed 38 people Wednesday has all the hallmarks of Jundallah, a Sunni Islamist group that has become a thorn in the side of the Shiite regime in Tehran.

The United States, in an apparent gesture toward Iran in advance of talks on Iran's contentious nuclear program last week in Geneva, branded the organization an international terrorist group Nov. 3.

The attack is likely to have internal repercussions in Tehran, with demands for iron-fist retaliation against the group that the regime has long claimed is funded, armed and directed by the U.S., British and Pakistani intelligence services to destabilize the Islamic Republic.

With Iranian President Mahmoud Ahmadinejad seemingly locked in an escalating power struggle with fellow conservatives, the attack in the port city of Chah Bahar on the Gulf of Oman could intensify tensions within the regime.

Although there was no claim of responsibility, the apparent use of multiple suicide bombers for a single attack is a tactic Jundallah, which means Soldiers of God, has used before.

The group carried out twin suicide bombings July 15 at a Shiite mosque in the provincial capital, Zahedan, that killed 28 people. The target apparently was a group of officers of the elite Revolutionary Guards Corps who were among the worshippers.

The corps, the regime's Praetorian Guard, has spearheaded Tehran's war against Jundallah and other rebel groups in border regions the regime maintains are aided by the Americans and Israelis.

In October 2009, a Jundallah suicide bomber killed at least 42 people in the town of Pishin in impoverished Sistan-Baluchistan, which borders Pakistan. The victims included five top-level Revolutionary Guard commanders, among them the deputy commander of the corps' ground forces.

That triggered a major crackdown against Jundallah, which culminated in the Feb. 23 capture of its leader, Abdolmalik Rigi, a charismatic young Baloch, by Iranian intelligence operatives in a complex operation.

According to Iranian reports, the Kyrgyz airliner he was flying from Dubai to Bishkek, the Kyrgyz capital, was forced down in Iran.

Rigi was executed June 20, and Tehran hoped that would put paid to Jundallah's eight-year insurgency.

Rigi was swiftly replaced as the group's commander by a veteran Islamist fighter identified as Mohammed Dhahir Baluch.

The Chah Bahar attack indicates the organization has regrouped and remains capable of deadly attacks directed against the regime and its Shiite adherents.

The July suicide bombings in Zahedan were Jundallah's response to Rigi's execution by hanging.

The group doesn't have known links with al-Qaida or the Taliban but a significant shift in its operations in late 2008 to tactics widely employed in Iraq and elsewhere indicated it had come under the influence of jihadist ideology.

In December 2008, Jundallah carried out its first suicide bombing, targeting a security forces headquarters in the town of Saravan. In May 2009, it carried out a suicide attack on a Zahedan mosque, its first major strike against a civilian target.

According to the U.S. global security consultancy Stratfor, the State Department's decision to place Jundallah on its terrorism blacklist represented "a huge gesture toward Iran."

It said Washington apparently "made the move in hopes of reaching an understanding on the balance of power in the Persian Gulf region after U.S. forces exit Iraq."

The move followed a series of diplomatic events, including "a preliminary understanding between Iran and the United States regarding a new power-sharing formula in Iraq in the form of a government led by incumbent Prime Minister Nouri al-Maliki, Washington seeking Iranian input in the process toward a settlement in Iraq, Iranian cooperation in Afghanistan, and Iran not creating instability in Lebanon."

The U.S. move may have been intended to refute allegations the CIA supported Jundallah and to distance itself from the group.

But independent analysts suggest Jundallah has received indirect U.S. support through Pakistan's Inter-Services Intelligence, which runs extensive covert operations along the Baluchistan border, or through Sunni-dominated Saudi Arabia, Shiite Iran's main geopolitical rival in the region.

"The Saudis have a hand in every Sunni group in the region," former CIA officer Philip Giraldi observed in July. "They're definitely players and may well be involved independently of the United States."