Russia said yesterday it had broken up Chechen rebel plans to attack towns in its turbulent north Caucasus region with poison and explosives, four days before world leaders hold wartime victory celebrations in Moscow.

A statement by the FSB state security services highlighted Russia's anxiety that high-profile celebrations marking the Soviet World War II victory over Nazi Germany could be disrupted by Chechen attacks.

Russian security forces have flooded Moscow with thousands of crack police units to deter possible attacks by Chechen fighters during a May 9 Red Square parade which will be attended by US President George W. Bush and other world leaders.

Media reported a string of bomb scares across Russia yesterday, but all so far have proved false alerts.

President Vladimir Putin, elected in 2000 vowing to wipe out Chechen resistance, has said he will never bow to rebel attacks.

"The FSB received information about the preparation of terrorist attacks during operations carried out to head off terrorist activity by Chechen bandit groups," a spokesman said.

The groups, based in Ingushetia which borders rebel Chechnya, had planned to use powerful cyanide-based substances in their attacks on towns in the seething north Caucasus and elsewhere, a statement said.

"The use of these strong-acting poisons in small doses in highly populated areas, key installations and in reservoirs could have caused a large number of victims," a statement said.

Separately, Interfax news agency quoted Chechen Interior Minister Ruslan Alkhanov as saying security forces had foiled a bomb attack in the Chechen capital Grozny planned for Monday and involving at least two female suicide bombers.

He said the women blew themselves up during a security raid.

The army said separate operations to head off rebel plans to sabotage the holiday stopped a truck carrying more than a tonne of explosives near Grozny.

No independent confirmation of the raids, or the details given, was available.

The FSB supplied photographs showing a small amount of explosives beside a truck. Separate pictures of the seized poison showed a man in a white coat holding a phial of clear liquid.