There has been a fresh upsurge of violence in the mainly Muslim North Caucasus as militants press ahead with a campaign against Kremlin rule.A suicide attack not far from a school in Chechnya’s capital Grozny has seriously injured three police officers. In Dagestan, Russian security forces killed four suspected rebels in a major military operation. And in Ingushetia, a suicide bomber blew himself up in a truck at a traffic police checkpoint, killing one other person and wounding several more. Recent violence has shattered a period of relative calm in the region where leaders say an Islamist insurgency has permeated all spheres of society. The growing turbulence has become a major headache for Moscow which fears the violence could spill over into other parts of Russia.