Russian security forces have arrested 30 people - including several security officers - on suspicion of helping the Chechen rebels who took 800 people hostage in a Moscow theatre.

We understand that the terrorist threat to Russia, including from outside, is increasing

Sergey Ivanov Russian Defence Minister

The suspects include security officials and political advisers, who are alleged to have colluded with the Chechen hostage-takers, who stormed the packed theatre last week demanding the withdrawal of Russian troops from Chechnya.

Russian media have been reporting that the rebels were briefed by security insiders about the authorities handling of the crisis.

More than 100 hostages died when elite troops regained control of the building by pumping a debilitating gas into the building and shooting dead most of the rebels.

The US ambassador to Moscow on Tuesday criticised Russia's refusal to name the gas it used - which proved poisonous and claimed the lives of at least 113 hostages - saying the secrecy cost lives.

'Unprecedented operation'

The Russian Interior Minister, Boris Gryzlov, said his forces were involved in an "unprecedented operation" to identify what he described as a terrorist network in Moscow and the surrounding region.

A government source, who confirmed to the BBC that security officials were among those arrested, said there had been far too many self-appointed 'helpers' milling about at the rescue headquarters.

A government-sponsored newspaper reported that the rebels had been briefed about what was going on outside by what it described as an "analytical centre".

The centre was collecting information from various sources - including the rescue headquarters - processing it and sending instructions to the fighters.

More than 200 survivors are still receiving treatment

A former commander of an elite special forces unit has also been quoted as saying that civil servants and security forces collaborators "helped the Chechen fighters to rent premises to store arms and explosives".

Liberal members of parliament are demanding an inquiry into the way the crisis was handled.

The Russian military has also intensified its operation against rebels in Chechnya itself, with reports that around 100 suspected militants had been detained in the republic in the past 24 hours.

But in a new setback, a Russian helicopter crashed near the main military base outside the capital Grozny, killing all four on board. Some reports said it was shot down by rebels.

Secrecy criticised

Questions are still being asked about the gas used in the hostage rescue operation, which claimed the lives of at least 113 hostages, but which the Russian authorities have refused to identify.

Theatre siege toll

Rebels shot dead: 41 Hostages killed by gas: 113 Hostages shot dead: 4 (at least 2 killed by rebels) Still in hospital: more than 300 In critical condition: up to 27

The American ambassador in Moscow, Alexander Vershbow, criticised the secrecy surrounding the gas, saying that if medical workers had a little more information about the gas a few more hostages might have survived.

Medical experts in Germany say siege victims being treated in Munich have shown traces of halothane in their blood and urine - an anaesthetic now rarely used in west European hospitals.

Earlier, the US embassy in Moscow said its physicians believed the opium-based gas fentanyl was pumped into the theatre.

Funerals

The first funerals of Moscow siege victims took place in and around Moscow on Tuesday.

Moscow Mayor Yuri Luzhkov honoured the victims

Families and friends gathered in the mud and drizzling rain to bury their dead, as more than 200 survivors continued to receive treatment in hospital for gas poisoning.

The BBC's Jonathan Charles in Moscow says the high death toll continues to make the raid controversial, but the strategy is now being studied by foreign intelligence agencies.

They are examining whether the deployment of gas might prove helpful if they are ever faced with similar sieges.

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