Moscow police have detained 150 migrants over suspicions of ties with Islamic militants, the Moscow Times reported Tuesday. The migrant workers were allegedly in possession of banned literature and other forbidden materials, but no weapons were found on them.

The report, which cited LifeNews, a pro-Kremlin source that has reported sensationalist stories in the past, comes amid a wave of jailings in Russia, where 500 migrant workers detained last week on suspicions of organizing robberies and attacks against women. Officials announced Tuesday that almost 2,000 people across Russia were held for terrorism-related reasons.

“A total of 1,756 persons are held in custody in the penal system for terrorist and extremist crimes, including 546 in pre-trial detention facilities, the rest in prison,” said Valery Boyarintsev, deputy director of the Russian federal penitentiary service.

Russians who participate in terrorist activities outside the country can be punished under Russian law. Boyarintsev said 246 people were in prison for being members of “illegal armed groups.”

Russian security forces reported foiling a large terrorist attack on Moscow’s public transit system earlier in October. Authorities said members of the group who plotted the attack in Moscow had trained with the terrorist group the Islamic State, also known as ISIS, in Syria.

The Russians have long feared terrorist attacks following the wars in Chechnya and a 2011 bombing at the Domodedovo airport in Moscow that killed 37 people. Officials say about 2,000 Russian citizens have joined the ranks of ISIS.

Russia began airstrikes in Syria in late September, saying they were targeting ISIS. But most of the raids have hit other opponents of Syrian President Bashar Assad, who is backed by Russia and opposed by the U.S.