MOSCOW, April 3 - RAPSI. Moscow's Khamovnichesky District Court will hear on April 16 the lawsuit filed by the Moscow Central District's Prosecutor's Office to declare as extremist a letter written by exiled oligarch Boris Berezovsky.

The letter was published by the Echo of Moscow radio station on its website.

Berezovsky earlier disseminated his letter calling on presidential candidates not to run for the presidency in the same pool as Putin.

The ruling party United Russia filed petitions with the prosecutor's office and the information watchdog to investigate the radio station for publishing the allegedly extremist letter.

Echo of Moscow Editor-in-Chief Alexei Venidiktov said he will propose organizing a joint legal group to examine the disputed letter if problems should arise.

United Russia said Berezovsky's letter contains calls to frustrate the presidential elections and violently overthrow the government. The ruling party maintains that Echo of Moscow violated the law on mass media by publishing extremist materials.

In turn, Venidiktov said he saw no signs of any calls for a forcible overthrow in the letter.

However, he later removed the letter from the website and handed it over to lawyers for a deeper analysis as some users regarded the letter as a call for a take-over.