They said a separate draw will be held to determine where and when the matches are played.
After a FIFA meeting in Rio de Janeiro last night, Blatter confirmed to The Guardian newspaper: 'We have decided on seeding the teams into two groups of four, taking the Fifa world rankings into account, with the top four in one pot and the others in another pot.'
'There will be a separate draw to decide home and away,' he added of the two-leg ties to determine four European places at the 2010 finals in South Africa.
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