Among the four militants was one of the closest associates of new Chechen rebel leader Doku Umarov. The Kamaz truck blew up during police special operation to liquidate rebels.
Umarov took over as Chechnya's new separatist leader last month after police killed Abdul-Khalim Sadulayev during a raid in an eastern Chechen town. Sadulayev's predecessor Aslan Maskhadov was killed in a police operation in March 2005, according to the AP.
Umarov vowed to widen attacks to the rest of Russia but also said rebel forces would focus on military and police targets rather than civilians.
The United States and NATO are conducting provocative activities both in airspace and waters of the Black Sea, Russian Defense Minister Sergei Shoygu said