Russian prosecutors have filed new murder charges against the former security chief of the country's troubled Yukos oil company.

Alexei Pichugin was already convicted last month for murder and an attack on a Moscow official, and sentenced to 20 years in prison.

Prosecutors said in the new charges that, in the late 1990s, he also organized the murder of a businesswoman and plotted two other killings.

They say the crimes were ordered by top Yukos shareholder Leonid Nevzlin, who lives in self-imposed exile in Israel.

Critics have denounced moves against Yukos as efforts to dismantle the oil firm in retaliation for the support its former chief, Mikhail Khodorkovsky, gave the political opposition.

Mr. Khodorkovsky was tried for tax evasion and fraud.  A verdict is expected April 27.

The government says it is cracking down on corporate crime.

Some information for this report provided by AFP and AP.