More Russians are fighting among the ranks of terrorist groups in Iraq and Syria than citizens from any other country, according to a new report published by an international consultancy group this week.

The New York-based Soufan Group’s findings published Tuesday focus on the threat posed by 5,600 jihadis returning to their homelands from conflicts in the Middle East.

The Soufan Group says around 400 out of the more than 3,400 Russian fighters have returned from battlefields in Iraq and Syria. Saudi Arabia and Jordan are the next highest sources of foreign terrorist fighters, followed by Tunisia and France.

President Vladimir Putin estimated this year that at least 4,000 Russians have joined terrorist groups in Syria. An additional 5,000 citizens of former-Soviet republics have joined their ranks, he said, citing Russian intelligence figures.

Kremlin spokesman Dmitry Peskov, when asked for comment on Thursday, cast doubt on the report’s findings, which cited Putin’s estimate.

“We don’t quite understand how much we can trust the given data, what basis they’re prepared on and what sources of information this organization has,” Peskov said.