He described European Central Bank chief Jean-Claude Trichet's warning that eurozone governments must keep a lid on borrowing as "noble".
"He's the head of the central bank - it's his job to say things like that," Mr Strauss Kahn said.
"We are in the biggest crisis we have experienced for 60 or 70 years and we have to take that into account," he added.
In November, the IMF lowered its global economic growth forecast to 2.2% from 3%.
In the BBC interview, Mr Strauss-Kahn was asked about the level of debt in the UK - 44.2% of GDP.
Shaun Ley, of BBC Radio 4's The World This Weekend, asked Mr Strauss-Kahn: "Markets seem to have made their own judgements about this: it is cheaper to get insurance against big multinationals like BP and McDonald's defaulting than it is to get insurance against UK government bonds going under. That is quite disturbing, isn't it, when a country is viewed in that way?"
"Yes, it is," Mr Strauss-Kahn said. "That is a good example of the fact that we are facing something which is almost unknown."
Last week, Mr Strauss-Kahn said the IMF could cut its 2009 forecast for China to around 5% amid an "unprecedented" global slowdown.
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