MOSCOW - Stepping up their accusations against Russia's largest oil company, Russian prosecutors said Friday that they were investigating the murder of several officials and businessmen who had disputes with the Yukos company.

Yukos' troubles began July 2, when a top shareholder, Platon Lebedev, was arrested while in a hospital on charges of defrauding the state in a 1994 privatization of a fertilizer company.

The probe, which was widely seen as politically motivated, gained momentum with prosecutors launching a 16-hour search in the company's offices last week and requesting past audits of Yukos from the Tax Ministry.

On Friday, the Prosecutor General's office said it was investigating seven separate cases against Yukos, including Lebedev's case, alleged tax evasion and five murder and attempted murder cases, the Interfax news agency reported.

In particular, the prosecutors are probing the 1998 murders of the local mayor in the Siberian city of Nefteyugansk, home to Yukos' oil fields, and the killings of two businessmen, the Interfax said.

The prosecutors are also continuing to investigate the case of Alexei Pichugin, a Yukos security officer, who is accused in a 1998 double murder in Moscow.

A separate case relates to the attempted murder of Yevgeny Rybin, the head of an Austrian company, in 1998.

In a statement carried by the Interfax news agency, the Prosecutor General's office said that the murder and attempted murder cases are united by "property disputes between the victims' official and private structures and the Yukos oil company," the Interfax ereported.

A spokesman for the Prosecutor General's office confirmed the report but refused to give any further details.

Yukos has denied the previous accusations. There was no immediate comment from Yukos on the new allegations.

The company chief executive and top shareholder, Mikhail Khodorkovsky, said the probe had resulted from "a struggle for power between different wings" of President Vladimir Putin's administration. He did not name anyone.

Putin hasn't commented directly on the Yukos probe, which has scared investors and caused a sharp downfall in the Russian stock market.