Russian President Dmitri Medvedev has called on prosecutors to act against corruption and extremist groups trying to exploit the country's economic crisis by sowing unrest.

The Russian leader told a meeting of top prosecutors they must eliminate corruption within their offices as well as local governments and other official agencies in the country.

He expressed concern over what he called the rise of extremism, which he said has increased threefold. He noted that more than 2,000 murders committed last year remain unsolved. He said tens of thousands of people are missing.

The president also criticized prosecutors for shoddy work and their inability to adequately present evidence to juries. He did not mention any particular case. But the comments followed the acquittal last week of three men charged with helping carry out the murder of investigative journalist and Kremlin critic Anna Politkovskaya.

Meanwhile, prosecutors have defended those handling the case and a top prosecution investigator, Alexander Bastrykin, insisted on the guilt of the three suspects, despite the jury's verdict.

A gunman shot and killed Politkovskaya, a vocal critic of Kremlin policy in Chechnya, in her Moscow apartment building in October of 2006.

Authorities have not apprehended the alleged shooter or anyone identified as ordering the killing.

Russian authorities introduced jury trials in the 1990s following the breakup of the Soviet Union. But the juries tend to acquit suspects at a much higher rate than when cases are heard by judges.

Some information for this report was provided by AP and Reuters.