The four are believed to have links to the banned Caucasus Emirate headed by veteran Chechen fighter Doku Umarov, who claimed responsibility for the suicide bombings on the Moscow metro in March 2010 and at Moscow's Domodedovo airport in January of this year.
Russian media subsequently quoted security service officials as identifying the four suspects as Murad Edilbiyev, from Grozny; Murad Umayev, from Ingushetia; Islam Khamzhuyev, from Kabardino-Balkaria; and Fyarid Nevlyutov, a resident of Mordovia.
They were reportedly apprehended in Moscow on July 5-6 on the basis of testimony by a militant arrested earlier.
They are said to have been in possession of weapons, a 10 kilogram improvised explosive device, and a map of one of their proposed targets. According to Bortnikov, the men have already named associates and possible accomplices.
Investigators think the four may have joined the Islamic insurgency after being influenced by the writings and video addresses of Aleksandr Tikhomirov (aka Said Buryatsky), a young convert to Islam who served as one of the Caucasus Emirate's main ideologists from the summer of 2008 until he was killed in a counter-terror operation in Ingushetia in March 2010. His homilies are widely circulated and reportedly hugely popular.
The hypothetical link between the four men and the Caucasus Emirate leadership is plausible considering Umarov's threats in the wake of the Domodedovo suicide bombing to launch more attacks of this nature on Russian transport infrastructure. In a brief telephone call to RFE/RL's North Caucasus Service in early April, Umarov similarly warned Russia's leaders that they "will hear from me again soon."
The most recent interview with Umarov posted on the Caucasus Emirate main website kavkazcenter.com was in mid-May.
Earlier this month, Kavkazcenter posted a video featuring Caucasus Emirate Qadi Sheikh Abu Muhammad, who said in response to a question that "according to the information at our disposal," Umarov is still alive.
Bortnikov's comments suggest the four suspects may have intended to employ the same tactics as Magomed Yevloyev, the Domodedovo suicide bomber, who was an Ingush.
In contrast to the overwhelmingly Chechen moderate insurgency wing, (which has reportedly inflicted dozens of casualties on pro-Moscow Chechen forces in heavy fighting in the south-eastern district of Vedeno over the past two weeks), Umarov's forces unite fighters from across the North Caucasus and elsewhere in the Russian Federation.