Andrew Harding: "The Mayor of Moscow said he's convinced this was a terrorist attack"

Interfax news agency said the two were detained on Friday on suspicion of involvement in the blast. They are expected to remain in police custody until Monday at the earliest.

Investigators say they are not ruling out links between the suspects and commercial organisations which had premises on the ground floor of the building where the explosion happened.

'Blood-thirsty enemy'

Russian Prime Minister Vladimir Putin went on national television to condemn the explosion.

"If it was a terrorist act, we are confronted by a cunning, brazen and blood-thirsty enemy," he said.

He said security services were investigating whether the blast was the result of negligence, criminal carelessness in handling explosive substances or a terrorist act.

Earlier Moscow Mayor Yuri Luzhkov visited the site and said it was "a complete certainty" that terrorists were to blame.

Search over

Mr Luzhkov said that rescue workers had completed their search of the rubble and the final death toll was 90.

Most people would have been asleep at the time of the explosion - 0012 local time on Thursday (2012 GMT Wednesday).

The blast led to the complete collapse of the central part of the eight-storey block in the south-east of the city. It also damaged 15 nearby buildings.

Residents return to collect belongings

Russia's security service has confirmed that some sort of explosive device was to blame rather than a gas leak, as initially suspected.

A preliminary investigation suggested an "industrial explosive device" or "a large amount of pyrotechnic devices" were to blame, it said, adding that the explosive power was equivalent to 300-400kg of TNT.

If confirmed as a bomb, it would be the third such attack in Russia in the past 10 days.

A blast in a shopping centre in central Moscow last week killed one person.

And at the weekend, a car-bomb attack killed scores in an apartment block in the southern Dagestan region, where Russian forces are fighting Islamic guerrillas.