Russian police and security agents detained 140 people at a mosque in Moscow on Friday on suspicion of involvement with Islamic extremism.
A statement from the Federal Security Service reported by Russian news agencies said that among those detained were 30 citizens of unspecified foreign countries.
The detentions come a week after the two suspects in the fatal Boston Marathon bombings were identified as Russian-born ethnic Chechens who sympathized with Islamic extremists.
There were no immediate reports of charges being filed. The security agency referred The Associated Press to a district office, where the telephone was not answered.
The reports cited the agency as saying the mosque previously has been visited by people who had been involved in preparing or carrying out terrorist attacks.
A Chechen separatist insurgency that began in the 1990s increasingly took on a fundamentalist Muslim character and spread to neighboring Russian Caucasus regions, including Dagestan, where Boston bombing suspects Tamerlan and Dzhokhar Tsarnaev and their family lived for a period before emigrating to the United States in 2002 or 2003.
The Tsarnaevs' parents later returned to Dagestan, and Tamerlan, who was killed in a shootout with police last week, made a long visit in 2012. Investigators are trying to find out details of what he did on the six-month sojourn, especially whether he met with any extremists.
Caucasus extremists have carried out gruesome attacks on civilians in Russia, including the 2004 seizure of a school in the town of Beslan that ended in the deaths of 330 people, about half of them children. They also claimed responsibility for the 2011 bombing of Russia's busiest airport, killing 36 people.
In 2011, U.S. authorities questioned Tamerlan Tsarnaev at Russia's request, but found nothing that sparked their interest and stopped watching him.
On Friday, officials briefed on the investigation told the AP that U.S. intelligence agencies had added the mother of the suspects, Zubeidat, to a government terrorism database 18 months before the bombings. The officials spoke to the AP on condition of anonymity because they were not allowed to speak publicly about the ongoing case.
The mother called the information "lies and hypocrisy" and said she had never been linked to crimes or terrorism.