President Dmitry Medvedev on Saturday called for police reform to help beat the "tumor" of Islamist violence in Chechnya and neighboring regions in the North Caucasus.

Medvedev arrived by helicopter for an unannounced visit to Nalchik, the capital of Kabardino-Balkaria. Medvedev has described a wave of violence in the North Caucasus as Russia's worst domestic political problem.

"Peace in the North Caucasus depends on how well-trained the law enforcement structures are," Medvedev said at a meeting with local officials, Interfax reported.

"We will part company with those who are not capable of working, irrespective of their merits. They must learn to work," he said.

Medvedev dismissed 18 high-ranking Interior Ministry officials recently and announced details of a national police-reform plan that is to include a 20 percent cut. A series of scandals has undermined the authority of the police force, which is ridden with corruption.

"Extremist bandit units still exist and have spread around as a cancerous tumor," Medvedev said Saturday. "They must be suppressed."

Violence is growing in the patchwork of mainly Muslim southern regions.

Authorities blame Islamist militants for most of the attacks, which often target security forces. Medvedev sent a new envoy to the North Caucasus this year to tackle the root causes of the unrest such as poverty and corruption. The North Caucasus Federal District chief Alexander Khloponin accompanied Medvedev on his trip Saturday.