Russia's main domestic security agency says that it arrested 12 people in the Kaliningrad region for suspected involvement with an Islamic extremist group.
Earlier on April 26, the Federal Security Service (FSB) announced the arrest of two suspected supporters of the Islamic State (IS) extremist group who it said were planning a "high-profile" terror attack in Russia's Far East.
The FSB alleged that the 12 detainees in Kaliningrad were involved with a group called Islamic Jihad-Jamaat Mujahedin and were of Central Asian descent. It said they may have been involved in militant recruiting activities.
The alleged leader of the cell was placed on a wanted list for extremist crimes by Uzbekistan, the FSB said, adding that it planned to deport the detainees shortly to their home countries for prosecution on terrorism charges. Human rights groups say suspects face potential abuse and torture when they are sent from Russia to Uzbekistan.
Kaliningrad, which is sandwiched between Poland and Lithuania, has strong military importance as Russia's westernmost territory and home to its Baltic Fleet.
It was at least the third time this month that Russia accused people with roots in the former Soviet republics of Central Asia of being involved in terrorist activity within its borders.
Russian authorities say a bombing that killed 16 people on a St. Petersburg subway train on April 3 was carried out by an ethnic Uzbek, Kyrgyzstan-born Russian citizen who was among the dead. They have arrested 10 people originally from Central Asia in connection with that attack.
The security agency said one of the two suspected IS supporters who were arrested on April 26 in Yuzhno-Sakhalinsk, a city on the Pacific island of Sakhalin, was from a Central Asian state that it did not name.
The other suspect in Sakhalin is a citizen of Russia, it said.
The FSB said a search of the two suspects' residence in Sakhalin turned up a homemade explosive device containing shrapnel, IS propaganda, and mobile phones with instructions for making bombs.
The agency said the two men were planning to carry out a "high-profile" terror attack targeting a crowded public place.
An FSB video of the suspects broadcast on Russian state television showed the two men handcuffed and lying face down on the floor.
IS claimed responsibility for an attack on an FSB office last week that killed two people in the city of Khabarovsk, also in Russia's Far East.
However, authorities denied that attack had any link to the militant group and said the assailant, a 17-year-old ethnic Russian who was shot dead, had ties to neo-Nazis.
Sakhalin Island, where the FSB said it foiled an impending IS attack, is known for its rich oil and gas fields, which have drawn billions of dollars of investment from Gazprom, ExxonMobil, Shell, and others major energy companies.
With reporting by AP, AFP, dpa, TASS, and Interfax