Iran tipped off Russia about the possibility of a major “terrorist operation” on its soil ahead of the concert hall massacre near Moscow last month, three sources familiar with the matter said.

In the deadliest attack inside Russia in 20 years, gunmen opened fire with automatic weapons at concertgoers on March 22 at the Crocus City Hall, killing at least 144 people in violence claimed by the Islamic State militant group.

“Days before the attack in Russia, Tehran shared information with Moscow about a possible big terrorist attack inside Russia that was acquired during interrogations of those arrested in connection with deadly bombings in Iran,” said one source.

Iran’s intelligence ministry said in January it had arrested 35 people linked to twin bombings on Jan. 3 in the southeastern city of Kerman that killed nearly 100 people. On Jan. 19, the ministry said it had arrested a commander of Islamic State’s Afghanistan-based branch ISIS-Khorasan (ISIS-K).

Islamic State claimed responsibility for the Iran blasts, the bloodiest since the 1979 Islamic Revolution. U.S. intelligence sources said ISIS-K had carried out both the Jan. 3 attacks in Iran and the March 22 shootings in Moscow.

Islamic State once occupied large swathes of Iraq and Syria, imposing a reign of terror and inspiring lone wolf attacks in Western countries, but was declared territorially defeated in 2017.

However ISIS-K, one of its most fearsome branches, has raised the group’s profile again with large-scale bloodshed.

ISIS-K, named after an old term for a region that encompassed parts of Iran, Turkmenistan and Afghanistan, emerged in eastern Afghanistan in late 2014 and quickly established a reputation for extreme brutality.

SIGNIFICANT OPERATION

A second source, who also requested anonymity due to the sensitivity of the issue, said the information Tehran provided to Moscow about an impending attack had lacked specific details regarding timing and the exact target.

“They (the members of ISIS-K) were instructed to prepare for a significant operation in Russia… One of the terrorists (arrested in Iran) said some members of the group had already travelled to Russia,” the second source said.

A third source, a senior security official, said: “As Iran has been a victim of terror attacks for years, Iranian authorities fulfilled their obligation to alert Moscow based on information acquired from those arrested terrorists.”

Iran’s foreign ministry and the Kremlin did not reply to a request for comment on this story. The White House had no comment on the matter.

A source familiar with the U.S. intelligence on an impending attack in Russia said it was based on interceptions of “chatter” among ISIS-K militants.

Challenging the U.S. assertions, Russia has said it believes Ukraine was linked to the attack, without providing evidence. Kyiv has strongly denied the assertion.

It is harder, however, for Russia to dismiss intelligence from diplomatic ally Iran on the attack, which raised questions over the effectiveness of Russian security services. Moscow and Tehran, both under Western sanctions, have deepened military and other cooperation since Russia invaded Ukraine in February 2022.

TAJIK NATIONALS

Both the attacks in Kerman and near Moscow involved Tajik nationals. ISIS-K has aggressively recruited from the impoverished former Soviet republic of Tajikistan, security experts say.

Sources said Iran had discussed its security concerns with Tajikistan. A diplomatic source in Tajikistan confirmed that Tehran had recently discussed with Dushanbe the issue of increased involvement of ethnic Tajiks in militant activities.

Islamic State harbours a virulent hatred for Shi’ites — Iran’s dominant sect and also the targets of its affiliate’s attacks in Afghanistan. It views them as apostates.

In 2022 Islamic State claimed responsibility for a deadly attack on a Shi’ite shrine in Iran that killed 13 people. Tehran identified the attacker as a Tajik national.

Earlier attacks claimed by Islamic State include twin bombings in 2017 that targeted Iran’s parliament and the tomb of the Islamic Republic’s founder, Ayatollah Ruhollah Khomeini.

(Inputs from Reuters)