London Mayor Ken Livingstone has backed Tube staff, who have walked out over safety concerns during the firefighters' strike.

He said he fully understood their "real genuine fear", but Downing Street condemned the action and said it was up to managers whether those not turning up for work should be disciplined.

London Underground said that 60 of its 505 trains were not running because drivers were refusing to work on safety grounds and staff shortages had forced the closure of two stations.

The total number of stations closed because of the strike is 24, and LU added 96 drivers had refused to perform their duties.

Stations closed on Thursday

Belsize Park Borough Caledonian Road Chalk Farm Covent Garden Edgware Road (Bakerloo Line) Elephant & Castle Gloucester Road Goodge Street Hampstead Holland Park Holloway Road Kennington Lambeth North Lancaster Gate Mornington Crescent Old Street Queensway Regent's Park Royal Oak Russell Square Shadwell (peak hours only) Tufnell Park Wapping

Mr Livingstone also condemned the government's handling of the firefighters' dispute and suggested that ministers have left the union with no option but to strike.

In an interview for BBC News 24, he said this week's pay offer of 11% was "irresponsible" because it was "guaranteed to provoke a strike".

Mr Livingtone said it was "appalling that people would die" but he "understood the anger" of the strikers.

As mayor of London, he has a role in negotiating the pay of firefighters in the capital. He insisted that employers had been prepared to offer a 16% rise, but had been "ordered" not to.

Downing Street strongly condemn the disruption to Underground services and said it was now open to the management to consider disciplinary action against the staff involved.

"The prime minister thinks that this is totally unacceptable. These lines should be open. They are not. That is causing enormous disruption to passengers," the prime minister's official spokesman said.

The spokesman warned there would be no justification for staff on the mainline rail network to take similar action to the Tube workers who were refusing to work.